erutceL setoN scisyhP in Edited by .J Ehlers, ,nehcn~LM .K Hepp, Z(Jrich .R Kippenhahn, M~inchen, .H Weidenm~iller, A. Heidelberg and .J Zittartz, n16K Managing Editor: W. BeiglbSck, Heidelberg 122 New Developments ni Semiconductor Physics Proceedings of the International Summer School Held in Szeged, Hungary - July 1 ,6 1979 Edited by .F Beleznay, G. Ferenczi, and .J Giber Springer-Verlag Berlin Heidelberg New York 1980 Editors Dr. Ferenc Beleznay Dr. Gy6rgy Ferenczi Research Institute for Technical Physics of the Hungarian Academy of Sciences 1325 Budapest, Pf. 76 Hungary Prof. Dr. J&nos Giber Institute of Physics of the Technical University of Budapest 1111 Budapest, Budafoki ut 8 Hungary ISBN 3-540-09988-3 Springer-Verlag Berlin Heidelberg New York ISBN 0-38?-09988-3 Springer-Verlag New York Heidelberg Berlin rights All to copyright. subject is work This era ,devreser or part whole the whether of the lairetam those specifically concerned, is of re-use reprinting, translation, of reproduction broadcasting, illustrations, yb or similar machine photocopying ,snaem dna storage n.i data .sknab § 54 the Under of namreG Copyright waL copies where era edam for a use, private than other eef is elbayap the the publisher, to tnuoma the of eef to eb determined yb tnemeerga the with publisher. © yb galreV-regnirpS Heidelberg 1980 Berlin in Printed ynamreG Printing dna binding: Beltz Offsetdruck, .rtsgreB/hcabsmeH 012345-0413/3512 PREFACE This volume consists of lecture notes and selected contributed papers presented at the International Summer School on New Developments in Semiconductor Physics held at the University of Szeged, July 1-6, 1979. The major part of the contributions in this volume is related to the new experimental technics and theoretical ideas applied in research of new semiconductor materials, mostly III-V semiconductors. We wish to thank the staff of the Department of Physics in the University of Szeged and of the Institute of Physics of the Technical University of Budapest for their cooperation in organizing this school and preparing this volume and Zsuzsa Nagy for her patient job of typing the manuscript. Budapest, January 1980, F. Beleznay J. Giber G. Ferenczi TABLE OF CONTENTS R.A. STRADLING: Low Temperature Photo- and Magneto-Transport Involving Impurity-Phonon Resonances in Semiconductors .......... I B.C. CAVENETT: Optically Detected Magnetic Resonance Studies of Semiconductors .............................................. 29 H.G. GRIMMEISS: Deep Level Spectroscopy in semiconductors by Optical Excitation ......... . ................................... 50 A. MIRCEA, D. PONS and S. MAKRAM-EBEID: Depleted Layer Spectroscopy ................................................... 69 C.M. PENCHINA: Luminescence of Chromium in Gallium Arsenide ......... 97 A. NOUAILHAT, G. GUILLOT, G.VINCENT, M. BALDY and A. CHANTRE Analysis of Defect States by Transient Capacitance Methods in Proton Bombarded Gallium Arsenide at 300 K and 77 K ..... ...107 G. FERENCZI: Properties of an Extended Defect in GaAs.62P.38 ....... 116 JiM. LANGER: Large Defect-Lattice Relaxation Phenomena in Solids...123 U. OGONOWSKA: Temperature Dependent Decay of a Metastable State of Systems with Large Impurity-Lattice Relaxation (CdF 2 : In) .150 J.T. DEVREESE: Electron-Phonon Interaction: Polaron Transport ...... 155 E.J. FANTNER: Stress Dependence of Quantum Limit Hall Effect and Transverse Magnetoresistance in n-InSb ........................ 176 I. KOSA-SOMOGYI, M. KOOS and V.A. VASSILYEV: Photoluminescence in Amorphous Semiconductors ................................... 189 G.A. SAI-HALASZ: Man-Made Semiconductors Superlattices ............. 215 F. GIBER: The Localized States of Interfaces and Their Physical Models ........................................................ 226 P. DEAK: Cyclic Cluster Model (CCM) in the CNDO Approximation for Deep Levels in Covalent Solids ............................. 253 J.T. WOLLMARK: Is There a Minimum Linewidth in Integrated Circuits? ..................................................... 263 LOW TEMPERATURE PHOTO- AND M~GNETO-TRANSPORT INVOLVING IMPURITY-PHONON RESONANCES IN SEMICONDUCTORS R.A. Stradling Physics Department University of St Andrews Fife KY16 9SS, U.K. ABSTRACT This paper reviews a number of resonance effects involving impu- rities and phonons. In a variant of the magnetophonon effect, electrons can loose energy from Landau levels by emitting L.O. phonons and being captured at impurities. This effect is demonstrated for n-Si and the intervalley phonons involved are determined. In the magneto-impurity effect inelastic scattering at the impurity takes the role of the optic phonons in the magneto-phonon effect. This effect and the im- purity capture effect are found with n-CdTe. With this material cap- ture at the n=1 and n=2 donor states is responsible for the series of deps in the photoresponse known as "oscillatory photoconductivity". Oscillatory photoconductivity involving the shallow donors is also de- monstrated for n-CdS. Oscillatory photoconductivity involving a number of excited states of several of the shallow donors has recently been reported for n-GaP. .I INTRODUCTION The first direct evidence that carriers could lose energy by emitting L.O. phonons while being captured at impurity sites came from the observation of a periodic variation of the photoresponse of diamond with the energy of the photon used to generate the photosignal (Hardy et.al. 1962). It was realised at that time the photocurrent would be quenched if the carriers found themselves at the correct energy to be captured at impurity states with the emission of one or more L.O. phonons. The period observed corresponded to the energy of the L.O. phonons (~coLO) and minima in the photoresponse were observed at photon frequencies (~) corresponding to ~00= N~tOLO + AE I )I( where A E 1 is the difference in energy between the ground state of the impurity and the excited state involved. Stocker (1966) considered the dynamics of the process where ~E I equalled the difference between the ground state of the impurity and the nearest band edge (i.e. the im- purity binding energy EI) . While studying the oscillatory photore- sponse of CdTe Mears et al. (1968) were the first to detect the in- volvement of the impurity ground state and therefore observed a process where AE I is zero in equation (I). The application of a magnetic field introduces the possibility of additional resonances as the band states become quantised into Landau levels. In this case further singularities in the photoresponse are expected when the carriers after photoexcita- tion from the impurity states and subsequent photoemission of N optical phonons find themselves in the mth Landau state. When this happens a minimum in the photoresponse occurs when ~U= NhtOLO + m~ to c + EI(B) )2( where oo c is the cyclotron frequency and E I is now dependent on the magnetic field B. A better known resonance effect which occurs without photoexcitation is the magnetophonon or Gurevich-Firshov effect (Gurevich et al 1963) which occurs when the carrier is scattered be- tween them and the m + nth Landalu level with the emission or absorption of L.O. phonons. In this case extrema are observed in the magnetore- sistance at magnetic fields given by flo0LO = n~ Ot c = nf eBn/m. )3( where B are the resonance fields and m ~ is the effective mass of the n band states concerned. In 1970 it was realised by Stradling & Wood that capture at impurity states was alternative process to the magnetophonon effect which was favoured at low temperatures. In this case peaks in the magnetoresistance could be observed at fields given by ~60LO = n~oo c + E l(B) )4( Transport processes involving resonances described by equations (I)-(4) have been reviewed by Harper et al (1973). A final resonance effect which can be observed in transport experiments is the magneto-impurity effect where an impurity is resonantly excited or de-excited by scattering carriers between Landau states so that AE I(B) = n~ Ot c )5( In equation )5( AE I can either be the energy between the ground and excited states of the impurity or the binding energy of the impurity. The magneto-impurity effect was first observed with n-InP (Eaves et al 1974) and has subsequently been reviewed by Eaves and Portal (1978, 1979). The present paper discusses some recent developments involving impurity-L.O, phonon resonances in semiconductors. 2. IMPURITY ASSOCIATED }{AGNETOPHONON RESONANCE IN n-TYPE SILICON Recently the first observation of magneto-phonon resonances as- sociated with impurity capture in n-type silicon has been reported (Portal et al 1979). The experiments were performed at lower tempera- tures (25-40 )K than thoseemployedin earlier magnetophonon studies of the inter- valley scattering in silicon (50-70 )K (Portal et al 1974, Eaves et al 1974). This is the first observation of such a process in a multi- valley semiconductor although the involvement of impurities in hot electron magnetophonon resonance has been well established in materials with conduction bands located at the centre of the Brillouin zone. (See review by Harper et al 1973). The additional complication in the present experiments is that the impurity capture processes involve in- tervalley phonons. Furthermore, in contrast to previous observations of the magneto-phonon effect associated with capture at impurities, (Harper et al 1973) the binding energies of the shallow donors are comparable to the phonon energies, and the binding energies are multi- valued due to the valley-orbit splitting of the ground state. In addition the several different phonons which are capable of relaxing electron energy by intervalley scattering, combine with the different Is donor states to give rise to many possible energy relaxation mechanisms. The energies of these resonant relaxation mechanisms are shifted to values which are typically between 2 and 10 times lower than the original phonon energies. This shift has enabled a more ac- curate determination of the phonon energies involved, together with the observation of additional phonons not previously detected in earlier magnetophonon experiments with silicon. The influence of uniaxial compressive stress has been studied, on both the series fundamental fields and the amplitudes of the oscillatory structure. The presence of uniaxial stress alters the resonance con- ditions through the change in the relative energies of the different conduction band minima. At large values of applied uniaxial stress all f-scattering processes, which occur between non-equivalent valleys, are completely suppressed leaving only g-scattering between the two conduction band mimina parallel to the applied stress. In addition the reduction in degeneracy of the conduction band minima changes the binding energies of the different Is donor states. IMPURITY CAPTURE RESONANCE CONDITIONS Magnetophonon oscillations were first observed in n-type silicon by Portal et al (1974). They observed resonances from electrons heated by the electric field out of equilibrium with the lattice, which was maintained at a fixed temperature between 55 K and 77 K. Six dif- ferent phonon scattering processes were found to contribute to the energy relaxation of the electrons. The multi-ellipsoidal structure of the conduction band in silicon leads to the possibility of intervalley scattering by either acoustic or optic phonons which may be between elli~soids with parallel princi- pal axes (g-scattering) or between ellipsoids situated along perpen- dicular crystals axes (f-scattering). in addition, the very aniso- tropic cyclotron masses produce a magnetophonon spectrum which varies markedly with the direction of the applied magnetic field. The simplest case occurs when B II~ h E II (111) and all six valleys are equivalent. Magnetophonon resonances will be determined for both f- and g-scat- tering by the relation Ne~ B hu3. (1) l m~11 where m111 is the cyclotron mass for B ,,11(111) With B II (100) and B II (110) the resonance conditions are more com- plex due to the non-equivalence of the six valleys. The condition for resonant f-scattering is e~ B (m + I/2) e~ B Z~i = (N + 1/2) ml m2 )2( for scattering between valleys with different cyclotron masses m I and m 2 and ~CO, - Ne~ B )3( l m 2 for valleys with the same cyclotron mass. Equation )2( describes energy relaxation from either transverse to longitudinal valleys or from longitudinal to transverse valleys and each of these processes will give rise to a set of magnetophonon series with differing phase. Thus there will be two periodicities produced in the Fourier analysis which are given by the relations A(I/B1)=e/m1~ o (M = const.) and A (I/B 2 = e/m200 o (N = const.) . For g-scattering the resonance condition is ~ _ Ne~ B (4) i ml, 2 For B II (I00) there are two longitudinal valleys with an effective mass m I = m± and there are four transverse valleys with a mass ar 2 =V--mm~m,,. In the case of B II (110) there are four longitudinal valleys with an effective mass given by I/m I I I I I/2 - (-T- + ) (5) V~ m i m± m I and there are two transverse valleys with a mass m 2 =mlV~ . In the analysis of the experimental data of the present paper the transverse cyclotron mass m t has been increased slightly from its low t~aperature value of O.1905 m to values between O.195 m (16OK) and 0.198 m o o o (34OK) to account for non-parabolicity within the conduction band (Stradling and Zhukov 1966, Ousset et al 1976) in the same way as was done by Eaves et al (1975) in order to obtain a good fit of their mag- netophonon data. Similarly the value taken for m I (0.90 m o) is slightly smaller than the band edge value of O.916 m o measured by Hansel and co- workers (Hansel et al 1965) but is more consistent with the observed anisotropy of the magnetophenon series. The experiments of Portal et al (1974) and Eaves et.al (1974, 1975) have shown that phonons of energies 14OK(g), 22OK(g or )f , 53OK(f) , 585K(f), 685K(f) and 745K(g) all give rise to the magneto- phonon series described by equations )I( to (5). Magnetophonon series associated with warm-electron energy re- laxation frequently involve capture at the ground states of shallow donor impurities, giving rise to oscillations determined by the re- sonance condition ~0o i = Nfo0 c + EI(B) )6( This mechanism was first demonstrated for GaAs (Stradling and Wood 1968) and has subsequently been verified for a number of semiconductors having conduction band edges located at the centre of the Brillouin zone (Harper et al 1973). As was shown by Nicholas and Stradling (1976) the amplitude of impurity-capture associated resonances is strongly temperature de- pendent. Accordingly the magnetophonon studies of Portal et al (1974) in n-type silicon have been extended to lower temperatures (~30 )K where the electrons just begin to freeze out. In this temperature region several magnetophonon series associated with electron capture at impurity sites have been observed. This process is qualitatively different in silicon as compared with that found in direct gap semi- conductors (Harper et al 1973), where the resonances occur from only one phonon, and the shallow donor energies are small compared with the phonon energy and are well described by the effective mass theory. In addition to complications in n-type silicon arising from the several different phonons which contribute to scattering for an arbirary di- rection of field, the effective mass theory for group V donors is in- adequate when applied to the Is ground state (Kohn and Luttinger 1955). The sixfold degeneracy for the states, originating from the six con- ducton band minima, is lifted in the case of the Is state, which splits into a singlet Is(At), a doublet Is(E), and a triplet Is(T1) . The nature of all three Is states is such that they contain con- tributions from all six conduction band minima. It is thus clear that impurity-capture associated magnetophonon series may occur in n-type silicon for all three Is states for both f- and g-type scattering processes and that these will both be determined by the relation ~ _ N e ~ B + E I )B( )7( i ml, 2 The following approximation for EI(B) may be used I e ~ B )8( EI(B) = EI(O) + 2 ml, 2 h~5 provided that ~ = 2E_(O) <I where EI(O) is the effective mass binding energy = 375°K. In t~e case of n-type sil'icon ~ = O.1 at 10 T for m t so that the oscillations will be accurately determined by the relation I e ~ B )9( ~i - EI(O) = (N + ~) mi,2 The Fourier analysis of such structure has been considered by Nicholas and Stradling (1976) and will give rise to a fundamental field given by