S.J.A. Adams

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.

UV laser assisted growth of molecular beam epitaxial ZnSe

Abstract Photo-assisted molecular beam epitaxy of ZnSe on GaAs substrates with UV irradiation is reported. The growth rate is observed to be a function of the layer thickness and at high UV levels growth can be totally supressed. Photo-assisted doping has been investigated for the first time in ZnSe and changes of up to 20x in the doping level are reported for iodine, n-type doped material. The results are discussed in terms of hole accumulation at the surface affecting the incorporation of selenium and iodine.

Electrical characterization of iodine doped molecular beam epitaxial ZnSe

We report the use of an electrochemical iodine cell to dope epitaxial ZnSe grown by molecular beam epitaxy (MBE) over a range of carrier concentrations from 1016 to 1019 cm-3. The doping levels throughout the layers have been measured by electrochemical CV profiling and calibrated in terms of the cell flux. Photoluminescence and Hall data confirm the growth of well behaved n-type ZnSe.

II–VI quantum-confined Stark effect modulators

Abstract The realization of p-doping with nitrogen of ZnSe and related alloys has enabled the development of quantum well laser structures. Similar structures can also be fabricated by MBE as optical modulators using the Stark effect on the exciton absorption. This is the first report of the growth and characterization of a ZnSe/ZnCdSe p-i-n quantum well modulator.

Photovoltage and carrier concentration profiles of ZnSe/ZnCdSe quantum well laser diodes

Abstract In this paper, we report the fabrication of ZnSe/Zn0.82Cd0.18Se quantum well laser structures on GaAs substrates using nitrogen and iodine as p- and n-dopants but without the use of an epitaxial GaAs buffer layer. The lasers show excellent mode structure and emit at 474.8 nm at 77 K in the pulsed mode. We have used recently developed electrochemical profiling techniques such as capacitance-voltage (C-V) measurements to determine carrier concentration profiles through the laser structure and photovoltage spectroscopy (PVS) to profile the bandgaps. In particular, the PVS profiling is invaluable for determining the compositions of the layers structures. This is the first time that such measurements have been obtained for II–VI laser structures.

Growth of MBE ZnSxSe1-x using a novel electrochemical sulphur source

Abstract In this paper we report the first successful use of an electrochemical sulphur source to grown ZnS x Se 1−x by the technique of molecular beam epitaxy. Photoluminescence measurements show that layers with 0⩽ x ⩽0.2 have been grown and that the material quality is comparable to that grown by other techniques.

Far-infrared optically detected cyclotron resonance in GaAs layers and low-dimensional structures

Novel far-infrared optically detected cyclotron resonance (FIR-ODCR) techniques are used to investigate GaAs epilayers and the results are compared with conventional cyclotron resonance performed at far-infrared frequencies and ODCR at microwave frequencies. The FIR-ODCR technique shows remarkable resolution and sensitivity and has been applied to investigations of the electronic structure of low-dimensional systems. In particular, cyclotron resonance has been optically detected in a GaAs/GaAlAs multiple quantum well (MQW) sample and compared with ODCR results performed at microwave frequency. Multi-single quantum wells (MSQW) in an MBE GaAs/GaAlAs structure with different well thicknesses have also been investigated, and by detecting cyclotron resonance via the FIR-induced changes in the luminescence of the separate wells, the power of the technique to investigate the cyclotron resonance mass versus well thickness in a single sample has been demonstrated. Finally, the experimentally determined values of effective mass for different well widths are compared with the theoretical results, showing good agreement.

Photoassisted molecular beam epitaxial growth of ZnSe under high UV irradiances

ZnSe has been deposited on (100) GaAs by molecular beam epitaxy under a uv irradiance of 4 W cm-2. At this level, the ZnSe growth rate can be severely reduced or stopped altogether. The authors show for the first time that the reduction in growth rate is a strong function of layer thickness for epilayers less than approximately 2000 AA thick. The growth rate under laser irradiation is found to be directly proportional to the Se flux, demonstrating that Se is the minority surface species even under high VI-II flux ratios. Furthermore they present observations indicating that the electron stimulated desorption of Se by RHEED beams and the photostimulated desorption are both due to the accumulation of photoinduced holes at the growth surface.

n-type doping of molecular beam epitaxial zinc selenide using an electrochemical iodine cell

The authors report the use of an electrochemical iodine cell to dope epitaxial ZnSe grown by molecular beam epitaxy over a range of carrier concentrations from 1016 to 1019 cm-3. The doping levels throughout the layers have been measured by electrochemical CV profiling and staircase doping structures have been used to calibrate the doping level in terms of the cell flux. Photoluminescence and Hall data confirm the growth of well-behaved n-type ZnSe.

Effects of UV laser irradiation on the growth of nitrogen-doped p-type ZnSe

Abstract Photoassisted p-type doping of ZnSe has been performed for the first time using active nitrogen doping and UV laser illumination of the growth surface. Above band-gap irradiation during growth results in a decrease in Se coverage, as is the case for n-type and undoped material, and this decrease in Se coverage allows higher nitrogen incorporation rates, although changes in ( N A − N D ) are relatively small at 280°C. From photoluminescence data we have identified the existence of a deep donor responsible for compensation in nitrogen-doped ZnSe.