H. Stewart

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.

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.

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.

Photoluminescence excitation spectroscopy of the lasing transition in ZnSe-(Zn,Cd)Se quantum wells

Abstract Photoluminescence excitation spectroscopy of the lasing transition in II–VI laser structures allows direct observation of the absorption edge during laser operation. We have investigated a set of Zn0.8 Cd0.2Se/ZnSe multiple quantum well structures with well widths ranging from 30 to 120 A and the photoluminescence at low excitation levels consistently shows the n = 1 heavy hole exciton transition, while above threshold the lasing peak is observed to be red-shifted with a localization energy which is always much greater than the Stokes shift due to inhomogeneities. Excitonic absorption features can be observed up to the highest excitation energies and the localization energy for all well widths remains around 30 meV suggesting that the optical gain above lasing threshold involves exciton-LO phonon emission.

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.

Low-temperature MBE growth of p-type ZnSe using UV laser irradiation

Abstract Photo-assisted 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 (NA − ND) 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.

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.