Y. Lansari

Improved ohmic contacts for p‐type ZnSe and related p‐on‐n diode structures

The problem of obtaining ohmic contacts for p‐type ZnSe is related to the deep valence band of ZnSe. We have addressed this problem by employing an epitaxial layer of the semimetal HgSe to decrease the interfacial energy barrier, or valence band offset, to about 0.6 eV. This has resulted in improved ohmic contacts for p‐type ZnSe films and related diode structures.

Electrical properties of p‐type ZnSe:N thin films

The van der Pauw Hall effect measurements from 77–350 K are reported for a series of p‐type nitrogen‐doped ZnSe thin films. Epitaxial HgSe electrodes were used as ohmic contacts in these experiments.

High-resolution study of stimulated emission from blue-green laser diodes

The first high‐resolution study of emission spectra from ZnSe‐based blue‐green laser diodes is reported.

p‐type modulation‐doped HgCdTe

At North Carolina State University, we have recently employed photoassisted molecular beam epitaxy to successfully prepare p‐type modulation‐doped HgCdTe. The modulation‐doped HgCdTe samples were grown on lattice‐matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this letter, we report details of the growth experiments and describe the structural, optical, and electrical properties that this new infrared quantum alloy of HgCdTe possesses.

Growth of HgSe and Hg 1− x Cd x Se thin films by molecular beam epitaxy

Thin epitaxial films of HgSe and Hg1−xCdxSe (x≤0.34) were successfully grown for the first time by molecular beam epitaxy. Film growth parameters are discussed, and results of structural, electrical, and optical studies are reported.

Electrical and optical properties of P‐ and As‐doped Cd1−xMnxTe

The introduction of phosphorus and arsenic dopants into bulk Cd1−xMnxTe crystals grown by the Bridgman–Stockbarger technique has been studied with respect to the resulting electrical and optical properties. Uncompensated acceptor concentrations as high as 1015–1016 cm−3 are obtained. Samples with a Mn composition in the range 0.10<x<0.30, both as‐grown and annealed, are studied. Hall‐effect and resistivity measurements are used to determine carrier concentrations, mobilities, and acceptor activation energies. A combination of room‐temperature transmittance and reflectance measurements over the spectral range from the ultraviolet to the far infrared has been used to gain information concerning structural quality and point defects. Low‐temperature photoluminescence measurements (1.6–5 K) are used to determine optical quality and excitonic energies. The effect of alloy broadening on luminescence linewidth is calculated and compared with measured values.

Electrical properties of modulation‐doped HgTe‐CdTe superlattices

Growth of modulation‐doped HgTe–CdTe superlattices (SLs) at very low temperatures (140 °C) by photoassisted molecular beam epitaxy is reported. SL layer thicknesses were intentionally chosen such that most of the SLs studied are inverted‐band semimetals or inverted‐band semiconductors. Both p‐ and n‐type samples were successfully prepared and studied. The doped superlattices exhibit excellent electrical properties. Lack of carrier freeze‐out at low temperatures provides convincing evidence that modulation‐doping has been achieved.

Light Emission from Quantum Well Structures Containing ZnS, ZnSe, and Related Alloys

Properties of blue and blue-green laser diodes with ZnCdSe single- and multiple-quantum-well active regions are discussed. Blue, blue-green, and green light emitting diodes which employ ZnCdSe or ZnSTeSe as the active region of double heterostructure devices have also been prepared and tested. Properties of ZnS-ZnSSe and ZnS-ZnCdS quantum well structures are also reported. These structures emit intense photoluminescence in the ultraviolet spectral region.

Modulation‐doped HgCdTe

At North Carolina State University, we have recently employed photoassisted molecular‐beam epitaxy (MBE) to successfully prepare p‐ and n‐type modulation‐doped HgCdTe. The modulation‐doped HgCdTe samples were grown on lattice‐matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this paper, we report details of the MBE growth experiments and describe the structural, optical, and electrical properties that this new infrared quantum alloy of HgCdTe possesses.

Light hole interband transitions in HgTe‐HgCdTe superlattices

The light hole to conduction band optical transition has been identified in the room‐temperature absorption spectra of several high quality HgTe‐HgCdTe superlattices, in addition to the familiar heavy hole to conduction band transitions. The observation of the light hole transition, coupled with a more accurate determination of the superlattice layer thicknesses, allows the superlattice band gap and the HgTe‐HgCdTe valence band offset to be determined more precisely than previously possible. A two‐band tight‐binding model was used to calculate the transition energies to compare with the optical data. The valence band offset for the HgTe‐Hg0.15 Cd0.85 Te interface was determined to be 300±25 meV.