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1 Aug 1969

Volume 40, Issue 9, pp. 3421-3886

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Power and Gain Characteristics of High Speed Flow Lasers

Terrill A. Cool

J. Appl. Phys. 40, 3563 (1969); http://dx.doi.org/10.1063/1.1658239 (11 pages) | Cited 26 times

Online Publication Date: 18 November 2003

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Output power and gain saturation characteristics are analyzed for a class of high speed flowing gas molecular lasers. Those flow lasers are treated for which laser action occurs within an optical cavity with an axis transverse to the flow direction, during the vibrational relaxation period following an initial excitation process that takes place upstream of the cavity. Performance predictions for an electrically excited fluid mixing CO2 laser based upon recent experimental measurements are presented. The concept of an ``equivalent nonflow laser'' is introduced which facilitates flow laser performance analysis in certain cases.

Study of Saturable Absorber Switching Efficiencies

A. Szabo and L. E. Erickson

J. Appl. Phys. 40, 3574 (1969); http://dx.doi.org/10.1063/1.1658240 (8 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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Theoretical and experimental studies of absorber switching efficiencies are described for a ruby laser operating at 77°K. The various operating regimes of absorber‐switched lasers are reviewed and the importance of inclusion in the theory of nonsaturable losses associated with the laser and absorber media is demonstrated. A particular dye‐host combination is found to have a markedly superior switching efficiency, the essential factor being a low residual loss under saturation conditions. The residual loss of vanadium phthalocyanine is shown to be host dependent and some tentative explanations of this are discussed.

Superconductivity in Niobium Containing Ferromagnetic Gadolinium or Paramagnetic Yttrium Dispersions

C. C. Koch and G. R. Love

J. Appl. Phys. 40, 3582 (1969); http://dx.doi.org/10.1063/1.1658241 (6 pages) | Cited 20 times

Online Publication Date: 18 November 2003

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Gadolinium and yttrium dispersions were prepared in pure niobium by solidification from the melt; the size, shape, and distribution of the particles were determined metallographically. The superconducting critical temperature and critical field of niobium were unaltered by the presence of the dispersions indicating that neither gadolinium nor yttrium have measurable solubility in solid niobium. Both gadolinium and yttrium dispersions produced large hysteresis in magnetization and large critical current densities. The degree of magnetic hysteresis produced in niobium by these dispersions has only been exceeded in niobium by fast neutron irradiation. Ferromagnetic gadolinium and weakly paramagnetic yttrium appear equally effective as flux pins. It is suggested that the nature of the particle superconducting matrix interface is more important for flux pinning than the bulk magnetic properties of the dispersed phases.

Effect of Substrate Imperfections on GaAs Injection Lasers Prepared by Liquid‐Phase Epitaxy

H. Kressel, H. Nelson, S. H. McFarlane, M. S. Abrahams, P. LeFur, and C. J. Buiocchi

J. Appl. Phys. 40, 3587 (1969); http://dx.doi.org/10.1063/1.1658242 (11 pages) | Cited 9 times

Online Publication Date: 18 November 2003

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A study was made of the correlation between substrate flaws and the performance of GaAs injection lasers fabricated by liquid‐phase epitaxy. These devices are p+∕n structures where the p+ region is deposited epitaxially, followed by heat treatment to displace the p‐n junction about 1–2 μ into the n‐type substrate. The melt‐grown substrates were studied with the aid of transmission electron microscopy, infrared transmission, x‐ray topography, etching studies, and photoluminescence. It is concluded that the dislocation density of the substrate is not the controlling factor in laser performance unless it exceeds 105 cm−2. A dislocation density of 103–104 cm−2 is not excessive. Precipitates and impurity striations in the substrate are probably the most damaging imperfections. In Te‐doped GaAs the presence of Ga2Te3 precipitates is to be avoided. In the case of Si‐doped materials, the precipitation problem appears to be less severe. Nevertheless, small clusters have been detected by electron transmission microscopy in the back portion of some melt‐grown ingots (furthest from the seed end). Their nature is unknown but they severely degrade laser performance. We show that a good correlation exists between the relative photoluminescence efficiency and laser performance. Thus, photoluminescence measurements are useful in the selection of Si‐doped substrates.

Domain Wall Profiles in Magnetic Films

M. S. Cohen and K. J. Harte

J. Appl. Phys. 40, 3597 (1969); http://dx.doi.org/10.1063/1.1658243 (14 pages) | Cited 8 times

Online Publication Date: 18 November 2003

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An inversion procedure for determining a domain wall profile from the associated Lorentz‐microscopy electron‐density distribution is discussed. This procedure is verified by application to computer‐simulated electron‐density distributions derived from assumed wall profiles. The experimental realization of the inversion procedure is demonstrated for high‐resolution Lorentz micrographs of films ranging in thickness from 100 to 500 Å; unreliable profiles were obtained for thicker films. The importance of correcting for the effects of nonmagnetically scattered electrons is emphasized; these effects increase with increasing sample thickness and defocussing distance. The experimental domain wall profiles exhibit first a rapid, then a slow increase of wall angle with distance from the wall center. Wall widths derived from these profiles are consistent with theoretical predictions if corrections are made for nonmagnetic scattering; if such corrections are not made, the large widths reported by other authors are obtained.

Stability of Ferromagnetic Domain Structures at Grain Boundaries

A. G. Tobin and D. I. Paul

J. Appl. Phys. 40, 3611 (1969); http://dx.doi.org/10.1063/1.1658244 (4 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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The magnetic domain structures formed at grain boundaries in recrystallized iron foils have been analyzed using Lorentz electron microscopy. Five basic types of domain structures have been observed at grain boundaries in iron: (1) Domain walls which penetrate through the boundary indicating ``no interaction,'' (2) double spike reverse domains, (3) single spike reverse domains, (4) echelon domains, and (5) domains of closure. Attempts to correlate the stability of the various domain types with the magnetic pole density of the grain boundary led to the following conclusions: (a) Double spike and ``no interaction'' domains appear to be associated with low pole densities while domains of closure appear to be associated with relatively larger pole densities and (b) no clear statement can be made with respect to the relative stabilities of the single spike and echelon domains due to difficulties in determining the magnetization direction within the domains and within the grain itself. They appear to overlap the pole densities of the other structures and each other as well. It is suggested that grain boundaries are important sources of reverse domain nucleation in polycrystalline ferromagnetic materials. The results emphasize the importance of the internal magnetostatic energy in determining the magnetic domain structure of iron.

Magnetic Susceptibility of β′‐NiAl

M. B. Brodsky and J. O. Brittain

J. Appl. Phys. 40, 3615 (1969); http://dx.doi.org/10.1063/1.1658245 (3 pages) | Cited 10 times

Online Publication Date: 18 November 2003

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The magnetic susceptibility has been measured for a number of NiAl compounds, ranging from 46.1 to 59.2 at.% Ni. The results were found to fit the expression, χ = (A∕T) + B between 6° and 300°K. Calculations of the temperature independent term fit the observed composition dependence up to 50 at.% Ni, but the composition dependence of that term is much higher for Ni contents above the equiatomic composition. Similarly, the value of A remains close to zero up to 50 at.% Ni and then rises over a small composition range to a large, composition independent value. The results above 50 at.% Ni are attributed to Ni☒Ni nearest neighbors, which cause short‐range magnetic order.

Magnetostatic Waves in Short, Axially Magnetized YIG Rods

M. F. Lewis and D. G. Scotter

J. Appl. Phys. 40, 3618 (1969); http://dx.doi.org/10.1063/1.1658246 (3 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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We have performed cw resonance and pulse‐echo measurements on magnetostatic waves in short, axially magnetized YIG rods which do, and do not, contain a turning point. The results are compared with a simple theory which includes the effects of the radial variation of the demagnetizing field. The agreement is generally satisfactory except for the magnetostatic mode spacing when the rod contains a turning point. In this latter case the agreement is only qualitative.

Effect of Inhomogeneity on Magnetic Properties, X‐Ray Diffraction and 31P NMR Linewidths in UP1−xSx Powders

Moshe Kuznietz, F. P. Campos, and Y. Baskin

J. Appl. Phys. 40, 3621 (1969); http://dx.doi.org/10.1063/1.1658247 (5 pages) | Cited 9 times

Online Publication Date: 18 November 2003

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The wide temperature range at which transitions occur between magnetic structures, and the coexistence of magnetic structures in the UP1−xSx system are attributed to the incomplete homogeneity of the powder samples. The inhomogeneity affects the linewidths of the x‐ray diffractometer traces, the 31P nuclear magnetic resonance (NMR) lines in the paramagnetic state, and the magnetic properties of UP1−xSx. The firing treatment of UP broadens the x‐ray lines, while a second homogenization of UP0.72S0.28 sharpens the x‐ray and 31P NMR lines and decreases the portion of the antiferromagnetic structure that coexists with the major ferromagnetic phase at low temperatures. The composition ranges (inhomogeneity widths) deduced from the x‐ray line broadening are about 0.1x0, where x0 is the mean sulfur concentration. The upper limits of the inhomogeneity widths obtained from the excessive 31P NMR linewidths and the widths of the magnetic transitions are in fair agreement with the inhomogeneity widths based on the x‐ray data.

Compilation of Elastic Wave Modes in Hexagonal Metals

Edmund G. Henneke and Robert E. Green

J. Appl. Phys. 40, 3626 (1969); http://dx.doi.org/10.1063/1.1658248 (7 pages) | Cited 1 time

Online Publication Date: 18 November 2003

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Elastic wave velocities, particle displacement vectors, and directions of energy flux have been calculated and are given as a function of the polar angle θ in the five hexagonal metals Be, Cd, Mg, Ti, and Zn. Because of elastic transverse isotropy around the hexagonal axis, the wave characteristics are functions of the angle between the hexagonal axis and the direction of propagation in the crystal only. The results of these calculations are especially useful for experimental investigations utilizing the ultrasonic pulse‐echo technique.

Orientation Dependence of Dislocation Damping in Hexagonal Metals

Edmund G. Henneke and Robert E. Green

J. Appl. Phys. 40, 3632 (1969); http://dx.doi.org/10.1063/1.1658249 (10 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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The orientation dependence of dislocation damping in the five hexagonal metals Mg, Cd, Be, Zn, and Ti has been predicted by calculation of the appropriate factors relating the stress field of the elastic waves to the slip systems in which the dislocations are moving. The four metals having basal slip systems have very similar qualitative behavior of the orientation factors. Titanium, with prismatic slip systems, has a quite different behavior and the orientation factors are smaller for all orientations than the values for the basal slip metals. For Zn, Cd, Mg, and Ti, the values of the orientation factors for standing waves (resonance technique) are larger than the corresponding values for the traveling waves (pulse‐echo technique). For Be, the orientation factors for both types of waves are nearly equal. Crystal orientations and wave types of particular interest for experimental study are delineated.

Experimental Investigation on the Blurring of Spatial Moiré Fringes

P. S. Theocaris, A. P. Vafiadakis, and C. Liakopoulos

J. Appl. Phys. 40, 3642 (1969); http://dx.doi.org/10.1063/1.1658250 (8 pages) | Cited 1 time

Online Publication Date: 18 November 2003

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An experiment was carried out on the intensity distributions resulting from the superposition of the images formed in the direction of each resultant order to the diffraction and optical interference pattern of a plane amplitude grating viewing a set of slits lying in a parallel plane. The experiment demonstrated the causes of blurring of the moiré fringes formed by two gratings separated by an air gap. From experiments conducted with pairs of identical amplitude gratings the blurring of spatial moiré fringes is demonstrated by microdensity tracings. It was found that the optical effects did not affect the interfringe spacing of the fringes.

Pulse Shape of Stimulated Raman Emission from an Oscillator Cavity

P. V. Avizonis and R. M. Heimlich

J. Appl. Phys. 40, 3650 (1969); http://dx.doi.org/10.1063/1.1658251 (7 pages) | Cited 3 times

Online Publication Date: 18 November 2003

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The time behavior of a pulse emitted by the stimulated Raman process (first vibration Stokes level in H2) is examined as a function of the Raman oscillator cavity parameter τ, the photon life time. Theoretical calculations of the Raman pulse shape, including laser depletion, using a linearized model of a standing wave are provided. Experimental comparisons to the calculations demonstrate satisfactory agreement for most measurements. The experiments were performed at 100 atm of H2, in order that antistokes be suppressed and calculations simplified.

Determination of the Low‐Frequency Electro‐optic Coefficients of NaNO2

A. R. Johnston and T. Nakamura

J. Appl. Phys. 40, 3656 (1969); http://dx.doi.org/10.1063/1.1658252 (3 pages) | Cited 4 times

Online Publication Date: 18 November 2003

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The unclamped electro‐optic coefficients were measured in ferroelectric NaNO2. The following values were obtained at 150°C, in units of 10−10 cm∕V: ra = r22 − (n3∕n2)3r32 = 4.1; rb = r32 − (n1∕n3)3r12 = 4.2; rc = r22 − (n1∕n2)3r12 = 0.6; r43 = − 1.9; r61 = − 3.0. The constants ra and rc vary approximately as ϵ2 does near the Curie temperature, as expected, but rb does not, decreasing toward zero at Tc. No significant temperature dependence was found in r61 or r43. The quantity ra changes sign as a function of temperature at 115°C. The observed behavior can be explained in terms of a temperature‐independent response including both second‐ and fourth‐order terms, biased by the spontaneous polarization.

Optical Activity and Birefringence Associated with Elastic and Plastic Deformation of the Alkali Halides

Roger Chang

J. Appl. Phys. 40, 3659 (1969); http://dx.doi.org/10.1063/1.1658253 (3 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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The optical activity and birefringence associated with elastic and plastic deformation of alkali halide single crystals were studied by means of transmission of monochromatic light in the visible region between crossed Nichols. Below the elastic limit, the optical axis is the direction of stress application. For permanently deformed crystals, the optical axes are the [110] directions regardless of the directions of original stress application, and the associated birefringence is shown to be dependent on the modes of plastic deformation. The origin for optical activity in both elastically and plastically deformed materials is not yet clear and is probably associated with perturbation by local electric or magnetic fields of charged dislocations present in the material under investigation.

Effects of Light on the Charge State of InSb☒MOS Devices

W. E. Krag, R. J. Phelan, and J. O. Dimmock

J. Appl. Phys. 40, 3661 (1969); http://dx.doi.org/10.1063/1.1658254 (7 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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We have made a detailed study of the effects of photon radiation in the energy range between 0.5 and 5.0 eV on InSb metal‐oxide‐semiconductor (MOS) devices. Measurements of the photocurrent through the MOS structures made at several temperatures showed that even at 300°K a photovoltage is developed for photon energies greater than about 1.3 eV. For photon energies above 3 eV the indium‐antimony oxide layer became photoconductive. The charging and discharging characteristics of the InSb‐oxide interface were investigated by measuring the response of the InSb☒MOS structure to modulated long wavelength (3.9 μ) radiation. This radiation acts as a probe for examining the band bending in the InSb at the InSb‐oxide interface, which in turn depends on the amount of charge trapped in the oxide or at the interface. When the MOS structure is irradiated with 1.3‐ to 4‐eV photons, the oxide and∕or the interface becomes negatively charged. At photon energies above 3.5 eV there is a competition between the mechanism which induces negative charge in the oxide and∕or interface region and the mechanism which releases this charge. This competition can be influenced by applied bias, and by properly biasing the device and irradiating with photons having energies greater than 4 eV the charges can be released.

Continuum Electrostatic Probe Theory for Large Sheaths on Spheres and Cylinders

R. E. Kiel

J. Appl. Phys. 40, 3668 (1969); http://dx.doi.org/10.1063/1.1658255 (6 pages) | Cited 25 times

Online Publication Date: 18 November 2003

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An approximate analysis is presented for spherical and cylindrical electrostatic probe operation under conditions such that large collision‐dominated sheaths are obtained. Analytical expressions are given for the sheath growth as a function of experimentally determined parameters. If pressure and temperatures are known, use of these results makes possible the direct interpretation of electron number density from a single probe measurement.

Temperature of a Laser‐Heated Carbon Plasma

C. D. David and H. Weichel

J. Appl. Phys. 40, 3674 (1969); http://dx.doi.org/10.1063/1.1658256 (6 pages) | Cited 8 times

Online Publication Date: 18 November 2003

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The temperature of a laser‐heated carbon plasma, formed by the interaction between a Q‐switched ruby laser and a pyrolytic graphite slab, has been measured using interferometric, spectroscopic, and energy conservation techniques. Results indicate that the maximum plasma temperature is less than 10 eV. A method of determining whether the plasma is in thermodynamic equilibrium is employed and indicates that at laser fluxes of 109 W∕cm2 the plasma is not in LTE with the electron temperature nearly an order‐of‐magnitude larger than the plasma temperature. For fluxes of 1010 W∕cm2, however, the plasma appears to approach a state of thermodynamic equilibrium with a temperature of 2eV.

Experimental Investigation of the Normal Modes in a Warm Cylindrical Plasma

N. Ben‐Yosef

J. Appl. Phys. 40, 3680 (1969); http://dx.doi.org/10.1063/1.1658257 (7 pages) | Cited 1 time

Online Publication Date: 18 November 2003

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Experimental observations of the normal modes in a cylindrical plasma without external excitation is presented. The experimental results compare favorably with theory. Measurement of the high‐frequency electromagnetic field outside of the plasma and its spectrum lead to a method of measuring the electrostatic oscillations spectrum in a plasma without perturbing it in any way. Exact measurement of the emission profile at the plasma frequency can give information about the mean thermal speed of the electrons without any assumption about their distribution function.

Characteristics of Rotationally Stabilized Long Plasma Arcs in a Chamber

Hsu‐Chieh Yeh and Wen‐Jei Yang

J. Appl. Phys. 40, 3687 (1969); http://dx.doi.org/10.1063/1.1658258 (7 pages)

Online Publication Date: 18 November 2003

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An analytical method is developed to determine the gas temperature distribution and the electric field strength‐arc length characteristics of a rotationally stabilized long plasma arc in a cylindrical chamber. The application of the method was demonstrated by numerical computations which were carried out for a monatomic hydrogen arc stabilized in a very large chamber. The relationships among the electric field strength, current, arc length, and arc‐axis temperature are disclosed.

Length Change of Copper and Aluminum after Electron Irradiation

R. Hanada, C. L. Snead, and J. W. Kauffman

J. Appl. Phys. 40, 3694 (1969); http://dx.doi.org/10.1063/1.1658259 (9 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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With the new application of capacitance‐change techniques, length‐change measurements were made in conjunction with annealing copper and aluminum specimens above their electron‐irradiation temperature of about 15°K. Damage rates at this temperature were also measured. The Stage I recovery of length change is compared with its resistivity counterpart. Remarkable correspondence is obtained to the degree that percentages of recovery of individual substages compare favorably, with the same defect inferred to be responsible for recovery in both cases. The production rate for length change was determined to be +1.8×10−23 cm2∕electron for 2.2 MeV electrons. Linear bending with dose was observed. This bending was analyzed as due to electron straggling. The ratio of resistivity change to volume change and to stored energy for electron and heavy‐particle bombardment shows good relative agreement. From the results, it was concluded that these physical‐property changes do not depend sensitively upon Frenkel pair close‐pair separation.

Electrical Behavior of Group III and V Implanted Dopants in Silicon

R. Baron, G. A. Shifrin, O. J. Marsh, and James W. Mayer

J. Appl. Phys. 40, 3702 (1969); http://dx.doi.org/10.1063/1.1658260 (18 pages) | Cited 85 times

Online Publication Date: 18 November 2003

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The anneal behavior of layers implanted with dopants from column III (B, Al, Ga, and Tl) and column V (As, Sb, and Bi) in silicon substrates has been investigated. The ranges of implant conditions were energy 20–50 keV, dose 1013–1015∕cm2, and substrate temperature 23°–500°C. Hall‐effect and sheet resistivity measurements were used to determine the effective number of carriers∕cm2 (Ns)eff and the effective mobility μeff. Analysis of nonuniform distributions of carrier densities and mobilities on these measurements shows that the values of (Ns)eff and μeff can be misleading unless the effect of the depth distributions is allowed for. These distributions have been determined in some cases by the use of layer removal techniques combined with Hall‐effect and sheet resistivity measurements. We find in well‐annealed implanted samples that the dependence of the mobility on carrier density follows that determined for bulk silicon. In many cases deviation from this relation can be accounted for on the basis of compensation. In the case of aluminum we suggest that this compensation may be accounted for by the presence of interstitial aluminum atoms acting as donors. We have found that interstitial thallium can behave as a donor. The anneal behavior of the implanted layer is influenced by ion species, dose, and substrate temperature. The carrier concentration measured in implantations of column III elements did not exceed the limits of thermal equilibrium solubility as is found for column V elements. In the former case, enhanced diffusion effects are observed. From the known substitutional behavior of column V elements, it is suggested that the anneal behavior in the 600°–800°C range is due to the dissociation of radiation damage complexes.

Electrical and Optical Properties of n‐Type Si‐Compensated GaAs Prepared by Liquid‐Phase Epitaxy

H. Kressel and H. Nelson

J. Appl. Phys. 40, 3720 (1969); http://dx.doi.org/10.1063/1.1658261 (6 pages) | Cited 26 times

Online Publication Date: 18 November 2003

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The radiative processes in Si‐compensated, n‐type GaAs prepared by liquid‐phase epitaxy have been studied by photoluminescence between 300° and 4.2°K. The data are consistent with the previous hypothesis of the formation under certain growth conditions of two types of acceptor levels by Si in GaAs (in addition to the shallow donor level) with ionization energies of ∼0.03 and ∼0.1 eV. Three basic radiative processes dominate at various temperatures: (a) Band‐to‐band recombination at 300°K, (b) conduction band (or possibly conduction‐band tail states) to shallow acceptor transitions at 4.2°K, and (c) conduction band to the deeper acceptor transitions at 77°K. The half‐width of the third emission band and its peak position depends on the Si and free‐carrier densities. The degree of compensation of these materials is a function of the substrate orientation. Of the three planes investigated, (100), (111)‐Ga, and (111)‐As, growth on the (111)‐As face results in the lowest degree of compensation. The present study shows that n‐type material with mobilities in excess of 1000 cm2∕V⋅sec and electron concentration in the 2–4×1018 cm−3 range can be prepared by growth at 1060°C with the advantage over Te‐ or Se‐doped GaAs that the formation of precipitates of Ga2Se3 or Ga2Te3 is eliminated. Such precipitates were previously shown to seriously degrade the radiative efficiency and hence the performance of injection lasers and spontaneous emitters.

Surface State and Interface Effects on the Capacitance‐Voltage Relationship in Schottky Barriers

C. R. Crowell and G. I. Roberts

J. Appl. Phys. 40, 3726 (1969); http://dx.doi.org/10.1063/1.1658262 (5 pages) | Cited 32 times

Online Publication Date: 18 November 2003

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In the presence of an interfacial layer and semiconductor surface states, a Schottky barrier height ϕb decreases with increasing electric field E at the surface of the semiconductor. If the semiconductor doping concentration Nd is uniform throughout the depletion region and if
math
where V is the applied voltage and ϵ is the semiconductor permittivity, the slope of the (capacitance)−2 vs voltage relationship is constant and can be interpreted to give Nd. The voltage intercept of the relationship yields an apparent barrier height ϕa related to the true barrier ϕb by ϕa=ϕb−E (dϕb∕dE) + (qNd∕2ϵ) (dϕb∕dE)2, where q is the electron charge. From the measured variation of ϕa with Nd and one absolute measure of ϕb at one value of Nd, ϕb(E), and dϕb(E)∕dE may be deduced. From dϕb(E)∕dE the surface state density as a function of energy in the bandgap and the minimum value of interface thickness divided by relative interface permittivity can be obtained. Using the data of Archer and Atalla for vacuum cleaved Au‐Si diodes to illustrate our method, the surface state density is found to peak at a value of ∼2×1014 cm−2⋅eV−1 at about 0.83 below the conduction band and the minimum value of interface thickness divided by relative dielectric constant is found to be of the order of 5 Å. Criteria are given which show how Schottky diode capacitance‐voltage data may be further used, in conjunction with photoelectric barrier measurements, to detect the presence of deep lying impurities or the penetration of surface state charge into the body of the semiconductor.

Optical Properties of n‐Type GaAs. I. Determination of Hole Diffusion Length from Optical Absorption and Photoluminescence Measurements

C. J. Hwang

J. Appl. Phys. 40, 3731 (1969); http://dx.doi.org/10.1063/1.1658263 (9 pages) | Cited 100 times

Online Publication Date: 18 November 2003

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Hole diffusion lengths L were determined for several Te‐doped GaAs crystals with electron concentrations ranging from 2×1016 to 6.5×1018 cm−3. The values of L were obtained by fitting experimental photoluminescence spectra to a theoretical expression which contains the measured absorption coefficients. This expression was derived from radiative recombination statistics, taking into account the reabsorption of emitted photons and the diffusion of minority carriers. The idea used by van Roosbroeck and Shockley of introducing the measured absorption coefficient by means of the principle of detailed balance is shown here to be valid for both nondegenerate and degenerate n‐type GaAs. It was found that the hole diffusion lengths are nearly independent of electron concentration n for n < 1×1018 cm−3. This result is attributed to a constant total hole lifetime associated with a nearly constant concentration of ``frozen‐in'' defects. For n > 2×1018 cm−3 values for diffusion length decrease rapidly with increasing n. This decrease is attributed to the formation of additional defects associated with donor complexes or precipitates, or both. The diffusion lengths determined in this work are in good agreement with those found by Wittry and Kyser from the electron‐beam excitation method but are larger than those obtained by Aukerman et al. from short‐circuit current measurements on n‐type surface barrier diodes subjected to high‐energy electron bombardment.
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