P J Dean

The nature of the predominant acceptors in high quality zinc telluride

Abstract We report very sharp bound exciton luminescence spectra in high quality melt-grown very lightly compensated ZnTe, p-type with N A - N D in the low 10 +15 cm -3 . Bound exciton localisation energies at seven shallow neutral acceptors with E A between ~55 and ~150 meV are very insensitive to E A . Optical absorption and dye laser luminescence excitation spectroscopy were necessary to obtain a full separation of the transitions due to different acceptors, together with a study of certain ‘two-hole’ luminescence satellites in which the acceptor is left in a series of orbital states after bound exciton decay. Two shallow acceptors are P Te and As Te , a third possibly Li Zn while a fourth, relatively prominent in our best undoped crystals, may be a complex. A deeper, 150 meV acceptor, frequently reported in the ZnTe literature and electrically dominant in most of our undoped crystals has the Zeeman character of a point defect. We present clear evidence from our spectra that this energy does not represent the binding of a single hole at a doubly ionized cation vacancy, a popular attribution since 1963. This acceptor may be covered by another impurity, possibly Cu Zn . We also report bound phonon effects, lifetime broadening of excited bound exciton states and observe a single unidentified donor with E D ~18.5 meV. This energy is determined using selective dye laser excitation at the weak neutral donor bound exciton line and from the onset of valence band to ionized donor photo-absorption.

The photoluminescence spectrum of bound excitons in indium phosphide and gallium arsenide

Photoluminescence spectra of refined epitaxial indium phosphide and gallium arsenide show clearly a close correspondence of bound exciton transitions. Classified in both materials are emissions due to excitons bound to neutral acceptors and donors, free exciton peaks and various types of phonon coupling. Excitons bound to neutral acceptors in both materials give rise to a sharp doublet emission which readily reveals the presence of strain in the sample. The magnitude of the strain is estimated to be approximately 10-3 in certain regions of typical epitaxial layers. Reflectivity experiments provide new estimates of the exciton gaps-1.4182 eV in indium phosphide and 1.5150 eV in gallium arsenide.

The location and shape of the conduction band minima in cubic silicon carbide

Abstract We have measured the inter-bound state excitation spectrum of the N C donor in cubic β-SiC through the ‘two-electron’ transition satellites observed in the luminescent recombination of excitons bound to neutral N donors. Transitions are seen to p as well as s-like donor states although the transition oscillator strength is derived from interaction with the impurity core since parity is conserved through inter-valley scattering by p-like X phonons. The Zeeman splitting of a luminescence line involving the 2p± donor state yield the electron mass parameter m t = 0.24 ± 0.01 m 0 . This and the directly measured energy separations of the 2p 0 and 2p± states yields m t / m 1 = 0.36 ± 0.01 with the static dielectric constant K = 9.92 ± 0.1. Mutually consistent central cell corrections of 1.1 and 8.4 meV are observed for the 2s(A 1 ) and 1s(A 1 ) donor states, the latter being in agreement with a recent estimate from electronic Raman scattering by Gaubis and Colwell. The ionization donor energy of the N C donor, 53.6 ± 0.5 meV is consistent with earlier, less accurate estimates from donor-acceptor pair and free to bound luminescence. There is no evidence for a ‘camels back’ conduction band structure in cubic SiC, unlike GaP. The two-phonon sidebands of the N C donor exciton luminescence spectrum in SiC can be constructed by X and Г phonons only.

Optical properties of undoped organometallic grown ZnSe and ZnS

Abstract Photo and cathodoluminescence of OM ZnSe and ZnS is very efficient at 4 and 300 K. The 300 K near gap luminescence is particularly strong for both materials compared to material grown by traditional techniques, and in ZnSe is much stronger than the deep centre luminescence. Variations in relative intensity of shallow and deep centre luminescence between layers are much larger for ZnS. The mechanisms and centres responsible for the major luminescence features are discussed and compared to CVD-grown non-epitaxial material of high purity. Dominant shallow donor appears to be Ga in ZnSe. The presence of the shallow Li acceptor has been established in ZnSe and of Cu in both ZnSe and ZnS. The deep centre luminescence is mainly self-activated at 300 K in ZnSe, but Cu-related luminescence is more prominent at 10 K in both materials and also appears in ZnSe even at 300 K. The higher energy form of the Cu-related distant pair luminescence is strongest, Cu-blue ZnS and Cu-green in ZnSe, in contrast to CVD and other high growth temperature material. Several unusual luminescence features are discussed, particularly an unexpectedly narrow band near 2.60 eV.

Donor discrimination and bound exciton spectra in InP

We report detailed studies of the near‐gap photoluminescence (NGPL) of refined vapor phase epitaxial (VPE) InP layers, selected to afford the best chance of resolving structure arising from the small chemical shifts between different donor species. Good general correlation was found between electrical data and the quality of the NGPL spectra in a survey of 50 crystals. In particular, the quality of the D+,X bound exciton (BE) and the ‘‘two‐electron’’ donor satellites (TEDS) of the D0,Xn BE luminescence components correlated with the 77 °K mobility, known to be dominated by ionized impurity scattering. Use of selective excitation with a narrowed line from a dye laser and magnetic fields to obtain spectral components less subject to inhomogeneous broadening is discussed. The magnetic field is most effective in narrowing the TEDS components. The crystal quality, expressed mainly through the total concentration of shallow donors and acceptors, is apparently just inadequate to obtain line narrowing by selectiv...

Photocapacitance effects of deep traps in epitaxial GaAs

A photocapacitance technique which allows rapid characterization of deep traps in a semiconductor is described. Continuous illumination with light of photon energy slightly below the band gap provides for the occupation of a trap level by both holes and electrons, and at the same time reduces the time constants associated with population changes to typically 0.1 sec. The first feature enables both hole‐emission and electron‐emission processes to be detected in a single spectrum and the second eliminates the effects of long time constants which could be masked by slow drifts. Sharp features due to individual traps are displayed by electronic differentiation with respect to energy of the photocapacitance signal. Thus we refer to the technique as double source differentiated photocapacitance (DSDP). Our data for deep levels in GaAs show that the variation of cross section with respect to energy is much more rapid than described by the frequently applied Lucovsky theory. This effect can be understood in terms...

Manganese doping of ZnS and ZnSe epitaxial layers grown by organometallic chemical vapour deposition

Abstract It is shown that tricarbonylmethylcyclopentadienyl manganese can be used successfully to dope thin films of zinc sulphide and zinc selenide grown by organometallic chemical vapour deposition, with manganese. The concentration of manganese in such layers has been investigated as a function of growth conditions and its distribution studied using secondary ion mass spectrometry. Cathodoluminescence and electroluminescence properties have been determined in an evaluation of manganese as a luminescence activator in these thin films.

Evidence for exciton binding at Ni impurity sites in ZnSe

Abstract A broad charge transfer band is observed in the photoluminescence excitation (PLE) spectrum of the 2.5 μ Ni2+ luminescence in ZnSe : Ni. This band lies above the highest energy d-d excitation bands and exhibits a ZPL at 1.8163 eV and LO(#38;0lambda;) phonon replicas at higher energy. In contrast, PLE spectra of Co2+ luminescence in ZnSe:Co contain only d-d excitation bands. The charge transfer band in ZnSe:Ni is interpreted as evidence for bound exciton formation at the Ni site. The recombination energy of this exciton is transferred efficiently to the excited d-band states of the Ni ion, leading to characteristic Ni2+ d-d luminescence.

Optical and capacitance spectroscopy of InP:Fe

Photocapacitance, DLTS, optical absorption and photoluminescence data are presented for iron- and iron-germanium-doped Czochralski single-crystal InP. The results demonstrate that the Fe2+ to Fe+ transition is not present within the InP band gap. A feature observed in photocapacitance and optical DLTS is attributed to the presence of the Fe4+ charge state, and features associated with the well known Fe3+ and Fe2+ states also occur. Photoluminescence measurements show an iron-related band near 0.5 eV, not previously reported in the literature.

Dye laser selective spectroscopy in bulk-grown indium phosphide

Donor-acceptor selective luminescence and luminescence excitation spectra of a specially refined InP crystal grown by the liquid encapsulated Czochralski technique are compared with results recently reported (Dean et al., 1979) for the common contaminant Zn. Carbon is the dominant acceptor in the new crystal with EA approximately 41.5 meV compared with (EA)Zn=48 meV. These excitation techniques provided by a tuneable dye laser provide clean resolution of several acceptor internal excitations whose transition energies are characteristic of the acceptor species, even though no useful information is available from the bound exciton spectra due to excessive spectral broadening. Transitions to two clearly resolved p states of the C acceptor yield p-state binding energies identical to those for the Zn acceptor while the binding energy of a single s state is a little less as expected. The high discrimination of the technique permits the probable identification of a second minor acceptor species as Zn.