J. Simpson

Compensation processes in nitrogen doped ZnSe

We have examined the compensation processes in nitrogen doped ZnSe grown by molecular beam epitaxy. Two independent donor–acceptor pair emission processes have been observed in photoassisted grown layers and detailed temperature dependence measurements have allowed us to conclude that a deep compensation donor with a binding energy of 44 meV exists in more heavily doped material. We propose that the compensating donor is a complex involving a native defect such as the (VSe‐Zn‐NSe) single donor and this suggestion is supported by the observation of changes in the carrier concentration profile with time.

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.

Electrochemical capacitance‐voltage profiling of n‐type molecular beam epitaxy ZnSe layers

We report the use of electrochemical capacitance‐voltage profiling of n‐type ZnSe layers by the use of NaOH electrolyte. Samples with both uniform and staircase doping profiles have been measured with concentrations ranging over 1016–1019 cm−3. The profiling technique has revealed in some samples regions of lower carrier concentration at the surface and at the ZnSe/GaAs interface. Our results demonstrate that this powerful technique can now be used for assessing the growth parameters of wideband gap II‐VI materials in the same way that is widely accepted for III‐V semiconductors.

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.

Electrochemical capacitance‐voltage profiling of n‐type ZnSe

In this article we report the first detailed study of electrochemical capacitance‐voltage profiling of ZnSe. An electrolyte consisting of 1 M sodium hydroxide and 1 M sodium sulphite has been developed that does not deposit selenium while etching the surface of n‐type ZnSe during C‐V profiling. The dissolution number of the electrolyte/ZnSe system is a function of the strength of electrolyte and the etching current and in order to obtain an accurate etching depth a constant etching current mode was used. A wide range of doping concentrations including both uniformly doped and staircase structures have been measured demonstrating that the electrochemical C‐V profiler can now be a routine tool for assessing the growth parameters of ZnSe.

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.

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.

Laser induced doping profiles in molecular beam epitaxy grown ZnSe doped with iodine

Abstract An optical projection system has been developed which allows patterning of both layer thickness and donor concentration in epitaxial films of ZnSe during growth by molecular beam epitaxy. Doping features with a period as small as 40 μ m have been produced and it appears possible to reduce this by at least one order of magnitude. Such in-situ techniques may be valuable for the fabrication of more sophisticated devices than are currently being produced from the wide-gap II–VI compounds.