K. A. Prior

Growth of zinc blende MgS/ZnSe single quantum wells by molecular-beam epitaxy using ZnS as a sulphur source

Zinc blende MgS has been grown on GaAs by molecular beam epitaxy using a novel method where the sources were Mg and ZnS. A reaction at the surface results in the formation of MgS layers with a Zn content estimated by secondary ion mass spectrometry and Auger spectroscopy to be between 0.5% and 2%. Double crystal x-ray rocking curve measurements of ZnSe/MgS/ZnSe layers show layers with good crystallinity. Using this growth technique layers up to 67 nm thick have been grown. Photoluminescence measurements of MgS/ZnSe/MgS single-quantum-well structures show that the confinement of the heavy hole excitons can be as large as 430 meV for a 1.7 nm well.

ZnSe‐ZnCdSe quantum confined Stark effect modulators

We report room temperature operation of a II‐VI p‐i‐n quantum confined Stark effect modulator using a ZnSe‐Zn0.8Cd0.2Se multiple quantum well structure within a ZdSe p‐n junction. A n‐type ZnSe layer was used as a novel contact to the p‐type ZnSe. Results are given for photovoltage spectroscopy, absorption, and differential absorption as a function of the applied electric field.

Epitaxial liftoff of ZnSe-based heterostructures using a II-VI release layer

Epitaxial liftoff is a post-growth process by which the active part of a semiconductor heterostructure, the epitaxial layer, is removed from its original substrate and deposited onto a new substrate. This is a well established technique in GaAs-based heterostructures where epitaxial liftoff can be achieved by exploiting the contrast in the etch rates of GaAs and AlAs in hydrofluoric acid. We report here successful epitaxial liftoff of a ZnSe-based heterostructure. We find that a metastable layer of MgS acts as a perfect release layer based on the huge contrast in the etch rates of ZnSe and MgS in hydrochloric acid. Epitaxial liftoff of millimeter-sized ZnSe samples takes a fraction of the time required for GaAs liftoff. Photoluminescence experiments confirm that the liftoff layer has the same optical characteristics as the original wafer material.

Optically detected magnetic resonance of deep centers in molecular beam epitaxy ZnSe:N

Optically detected magnetic resonance has been used to investigate the deep level recombination processes in p‐type ZnSe grown by molecular beam epitaxy and doped with nitrogen. In addition to the well‐known shallow donor resonance at g=1.11, an anisotropic deep donor resonance is observed with g=1.38 and a deep acceptor resonance is detected at g=2. These results are consistent with the pair recombination processes proposed by us previously where the compensating deep donor was assigned to the VSe‐Zn‐NSe complex.

Blue stimulated emission from a ZnSe p‐n diode at low temperature

Laser diode structures have been fabricated using molecular beam epitaxy with iodine from an electrochemical source for the n‐type doping and nitrogen from a plasma source for the p‐type doping. CV profiling using electrochemical etching shows uniform p doping of 4×1017 cm−3 and n doping of 1×1018 cm−3. Under pulsed current excitation blue emission at 470 nm is observed at room temperature which increases in intensity at liquid helium temperatures. Above a current density threshold of 50 A cm−2 stimulated emission is observed between 448–473 nm with a complicated mode structure.

Photoluminescence decay measurements of n‐ and p‐type doped ZnSe grown by molecular beam epitaxy

Time‐resolved photoluminescence has been used to study carrier recombination in n‐ and p‐type doped ZnSe at room temperature. A band‐edge photoluminescence decay time of ∼240 ps has been measured for heavily doped n‐type material together with a relaxation time of a few microseconds for the associated deep‐level emission. The band‐edge photoluminescence decay time for p‐type doped material was ≤11 ps and is indicative of a high level of nonradiative Shockley–Read recombination.

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.

Characterization of MBE grown II–VI semiconductor thin layers by X-ray interference

X-ray interference (XRI) is a simple and powerful technique used to characterise thin layers buried within epitaxial films of GaAs/AlGaAs and InGaAs/GaAs. XRI measurements are double crystal rocking curves made on structures of the type A/B/C/B, where A is the substrate, B a different semiconductor and C the thin layer of interest, (possibly the same as A). B/C/B forms an X-ray interference film with the thicknesses of B much greater than that of C. Here, the Pendellosung fringes from B are strongly modulated by the introduction of C. XRI is also ideal for investigating materials which can not be grown thick enough for DEKTAK measurements, in which the lattice constant is not known accurately, or the layer is unstable in air and must be capped.

IDENTIFICATION OF VSE-IMPURITY PAIRS IN ZNSE:N

Optically detected magnetic resonance (ODMR) of heavily nitrogen‐doped ZnSe at 24 GHz reveals an anisotropic spectrum which can be assigned to a deep donor comprised of a Se vacancy paired with an impurity. The newly resolved spectrum is trigonal along 〈111〉 with g∥=2.0072(2) and g⊥=2.0013(2). Comparison of this g tensor with previous work leads to the assignment of the spectrum to VSe‐X, where X is most probably Cu or Ag. Combining this result with previous photoluminescence and ODMR work shows that ZnSe:N has three distinct donors which include both impurities and intrinsic defects.