G.D. Brownlie

Compensating acceptors and donors in nitrogen δ-doped ZnSe layers studied by photoluminescence and photoluminescence excitation spectroscopy

The compensating acceptors and donors in nitrogen δ‐doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen rf‐plasma source are studied by means of photoluminescence (PL) and photoluminescence excitation spectroscopy (PLE). The temperature dependence of PL and PLE spectra obtained from the nitrogen δ‐doped layers is investigated in detail, and a deep acceptor and a deep donor with ionization energies of ∼170 and ∼88 meV are reported for the nitrogen δ‐doped layers. These two deep centers are assigned to N clusters, i.e., NSe‐Zn‐NSe for the deep acceptor and NSe‐NZn for the deep donor.

Microprobe Raman study of the variation of LO phonon frequency with the Cd concentration in the ternary compound Zn1-xCdxSe

Abstract Experimental and theoretical studies of II–VI and III–V ternary alloys suggest that the long wavelength optical phonons exhibit one of two types of behaviour, single or double mode. A semi-empirical model which has had success in predicting LO and TO phonon frequencies for mixed alloys is the random element isodisplacement model (REIM). Using a modified version of this model we have predicted that ZnCdSe will be of single mode type, and have calculated LO phonon frequency shifts with composition. Room temperature microprobe Raman measurements on samples of MBE grown Zn1 − xCdxSe with x ranging from 0 to 0.35 show a linear variation of a single LO phonon peak with composition, confirming our predictions, with good agreement with theory for low mole fraction of cadmium.

Compensating processes in nitrogen δ-doped ZnSe layers studied by photoluminescence and photoluminescence excitation spectroscopy

Abstract The compensating acceptors and donors in nitrogen δ-doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen rf-plasma source are studied by means of photoluminescence and photoluminescence excitation spectroscopy. A deep acceptor and a deep donor with ionization energies of ∼ 170 and ∼ 88 meV are reported for the nitrogen δ-doped layers. These two deep centres are assigned to N-clusters, i.e., N Se ZnN Se for the deep acceptor and N Se N Zn for the deep donor.

Piezoelectric effect in ZnSe/ZnCdSe quantum wells grown on (211)B GaAs

The piezoelectric effect has been demonstrated for the first time in strained ZnSe/ZnCdSe quantum wells grown on (211)B GaAs substrates. A piezoelectric field strength of 1.1 X10 5 V/cm has been observed in Zn 0.8 Cd 0.2 Se quantum wells that have a 1.3% lattice mismatch with the substrate.

Growth of sulphur-based ternary and quaternary epilayers for use in multilayer devices

We report the use of a valved cracker cell for sulphur in the growth of doped and undoped ZnSSe and ZnMgSSe lattice matched to GaAs for use in multilayer device structures. The cell provides fast flux changes allowing adjacent layers with differing S contents to be produced with a single S source without interruptions in the growth. Material grown using elemental sulphur shows good morphology with both high-quality photoluminescence spectra and X-ray double-crystal rocking curves.

Photoluminescence excitation spectroscopic studies of nitrogen doped ZnSe

Photoluminescence excitation spectroscopy (PLE) of nitrogen doped ZnSe epilayers is reported here for the first time. The dependence of the PLE spectra on the net acceptor concentration in ZnSe:N and the temperature has been investigated. A new radiative transition at 2.732 eV is revealed in highly doped ZnSe:N, and is attributed to a transition between the valence band and a new donor level with an ionisation energy of 88 meV. The effect of strain on the exciton spectra in undoped and N-doped layers is discussed.

Nitrogen doping during atomic layer epitaxial growth of ZnSe

This letter reports the growth and characterization of ZnSe:N layers by atomic layer epitaxy (ALE) using a nitrogen rf‐plasma source. The ALE‐grown ZnSe:N layers have been investigated in terms of in situ reflection high electron energy diffraction and ex situ capacitance–voltage profiling and photoluminescence spectroscopy. The net acceptor concentration in the ALE‐grown layer has been obtained as high as 1.2×1018 cm−3 and the ALE layers of ZnSe:N show reduced number of compensating deep centers compared with the ZnSe:N grown by molecular beam epitaxy. The effects of the Fermi level at a growing surface on the generation of compensating donors with a binding energy of 57 meV are also discussed.

DLTS and drift mobility measurements on MBE-grown nitrogen-doped ZnSe

Abstract We have studied nitrogen-doped ZnSe layers grown on p-GaAs substrates by MBE using deep-level transient spectroscopy and admittance spectroscopy. A hole trap with activation energy E v + 0.11 eV is attributed to a nitrogen acceptor which controls the p-type conduction in the materials. The drift mobility was measured using a time-of-flight technique. Values ranging from 5 to 80 cm 2 /V s were obtained at room temperature, depending on doping level.

Electrical characterization of hole traps in p-type ZnSe and ZnSSe grown by molecular beam epitaxy

Using deep-level transient spectroscopy (DLTS) and admittance spectroscopy we investigated nitrogen doped ZnSe and ZnSSe layers grown on p-type GaAs substrates by molecular beam epitaxy. Three major hole traps denoted T1, T2, and T3 were observed with energy levels at 0.11, 0.46, and 0.56 eV from the valence band, respectively. Similar energy levels were observed in nitrogen doped ZnSSe except that T1 was at 0.12 eV from the valence band. A crude estimation of the 0.11 eV trap concentration obtained from DLTS data shows correlation with the free carrier concentration due to nitrogen. We attribute T1 to a nitrogen acceptor which controls the p-type conduction in the materials. No other direct observations of this important acceptor level have been reported in the literature so far. The two remaining levels may originate from the nitrogen doping process. We also point out the effect of the series resistance observed in this kind of material.

Compensation in p-type ZnSe based semiconductors

Abstract Over the past few years nitrogen has been shown to be by far the best dopant to use in the production of p-type ZnSe, although it is often highly compensated. This review describes the evidence for compensation in ZnSe:N due to the presence of selenium vacancy complexes and also more recent evidence for the presence of other compensating donors and deep acceptors. The use of hydrogen plasma exposure to reduce the concentrations of these complex species is discussed. Various models have previously been presented to explain the compensation of ZnSe, and here we discuss the role of surface states in the pinning of the Fermi level and its effect on compensation. Finally, we show that the compensating selenium vacancies have been found by many authors to be mobile and discuss the mechanisms which may account for this behaviour.