G. Horsburgh

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.

Room temperature ZnSe/ZnCdSe bistable self‐electro‐optic effect device operating at 488 nm

Optical bistability at room temperature has been observed for the first time in a II‐VI semiconductor self‐electro‐optic effect device fabricated by molecular beam epitaxy. The optical switch is based on a ZnSe/ZnCdSe multiple quantum well structure situated within a p‐n junction and the devices operate at 488 nm in the blue‐green spectral region.

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.

Carrier recombination studies of ZnCdSe/ZnSe single quantum wells grown by molecular beam epitaxy

Temperature dependent time‐resolved photoluminescence has been used to study the excess carrier recombination in Zn0.75Cd0.25Se/ZnSe single quantum well structures grown by molecular beam epitaxy. For temperatures <100 K radiative excitonic recombination appears to dominate, and the photoluminescence (PL) decay time follows the linear dependence on temperature over the range 50–120 K. At higher temperatures the reduction in PL efficiency and decay time indicate that nonradiative processes associated with the ZnCdSe/ZnSe interfaces dominate the recombination. The results are consistent with theoretical predictions.

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.

Compensation processes in molecular beam epitaxially grown zinc selenide doped with nitrogen

Abstract Recent work has shown that nitrogen produced in a plasma source is a p-type dopant in MBE grown ZnSe with N a − N d to 1×10 18 cm -3 , but at these concentrations the material is highly compensated. In a previous study, we have examined the PL spectra of nitrogen doped material grown in our laboratory and have shown that there are two sets of donor-acceptor pair (DAP) peaks which can be explained by a simple model involving a nitrogen acceptor and two donors. The first donor is a native shallow donor and the second is a nitrogen related compensating donor thought to be a complex of the form V Se -Zn-N Se . Optically detected magnetic resonance results on samples showing both shallow and deep DAP luminescence show signals due to the shallow isotropic donors and deep anisotropic donors consistent with our proposed model. Calculations of the vacancy concentrations and degree of compensation that should be expected in nitrogen doped ZnSe show that at all temperatures and under all growth conditions the material is highly undersaturated with vacancies. The barriers operating to prevent the compensation are discussed.

Electron beam pumping of CdZnSe quantum well laser structures using a variable energy electron beam

In this paper we present experimental results on electron beam pumping of MBE and MOVPE lasers with CdZnSe single quantum wells. Laser emission in the green and blue occurs under pulsed excitation, with threshold power densities typically less than 2 kW/cm 2 at low temperatures. Threshold curves obtained at different electron beam energies show that there is an optimum electron beam energy for wells at a given depth below the surface. This suggests that it is possible to match the electron beam energy to a given structure. Results are broadly consistent with Monte Carlo calculations of the depth dependence of the energy deposition of the electron beam.

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.

A ZnSe/ZnCdSe quantum well symmetric self-electro-optic effect device operating in the blue-green region

Abstract In this paper, we report the first observation of a II–VI symmetric self-electro-optic device (SEED) operating as an optical switch at a wavelength of 488 nm at room temperature. Quantum confined Stark effect modulators based on ZnSe/ZnCdSe p-i-n structures were fabricated by molecular beam epitaxy and used in the symmetric mode where one modulator was used to bias a second modulator which showed bistable transmission characteristics with a contrast ratio of 1.5:1 between the high and low transmission states.

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.