R. L. Gunshor

Blue‐green injection laser diodes in (Zn,Cd)Se/ZnSe quantum wells

Laser diode action in the blue‐green has been observed from (Zn,Cd)Se quantum wells within ZnSe/Zn(S,Se) p‐n heterojunctions up to 250 K. Operation is reported for two different configurations for which the GaAs substrate serves either as the n‐ or p‐type injecting contact. In pulsed operation, output powers exceeding 0.6 W have been measured in devices prepared on both n‐type and p‐type GaAs epitaxial buffer layers and substrates.

Graded band gap ohmic contact to p-ZnSe

We describe a low‐resistance quasi‐ohmic contact to p‐ZnSe which involves the injection of holes from heavily doped ZnTe into ZnSe via a Zn(Se,Te) pseudograded band gap region. The specific contact resistance is measured to be in the range of 2–8×10−3 Ω cm2. The graded heterostructure scheme is incorporated as an efficient injector of holes for laser diode and light emitting diode devices, demonstrating the usefulness of this new contact scheme at actual device current densities.

Blue and green diode lasers in ZnSe‐based quantum wells

Laser diode operation has been obtained from (Zn,Cd)Se/ZnSe and (Zn,Cd)Se/Zn(S,Se) quantum well structures in the blue and the green. The devices, prepared on p‐ and n‐type (In,Ga)As or GaAs buffer layers for lattice matching purposes to control the defect density, have been operated at near‐room‐temperature conditions and briefly at room temperature with uncoated end facets. Quasi‐continuous wave operation has been obtained at T=77 K.

Microstructure study of a degraded pseudomorphic separate confinement heterostructure blue‐green laser diode

The microstructure of a degraded II‐VI blue‐green laser diode based on the ZnCdSe/ZnSSe/ ZnMgSSe pseudomorphic separate confinement heterostructure has been examined by transmission electron microscopy. Triangular nonluminescent dark defects observed in the laser stripe region by electroluminescence microscopy have been identified to be dislocation networks developed at the quantum‐well region. The dislocation networks have been observed to be nucleated at threading dislocations originating from pairs of V‐shaped stacking faults which are nucleated at or near the II‐VI/GaAs interface and extending into the n‐ZnMgSSe lower cladding layer.

High resolution electron microscope study of epitaxial CdTe‐GaAs interfaces

CdTe films have been grown on (100) GaAs substrates with two different epitaxial relations: (111)CdTe∥(100)GaAs and (100)CdTe∥(100)GaAs. High resolution electron microscope observation of these two types of interfaces was carried out in order to investigate the role of the substrate surface microstructure in determining which type of epitaxy occurs. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin layer (∼10 A in thickness), which is most likely an oxide, between the two crystals. These observations suggest that the GaAs substrate preheating cycle prior to CdTe film growth is crucial in determining which type of epitaxy occurs in this system.

New class of materials for optical isolators

Experimental measurements are presented to demonstrate the isolator capabilities of a new class of magnetooptic materials called dilute magnetic semiconductors. The specific sample used is Cd0.55Mn0.45Te, and it is shown to exhibit significantly better performance than other magnetooptic materials available for use at wavelengths shorter than 1.0 μm.

Zinc-blende MnTe: epilayers and quantum well structures

Epilayers of the previously hypothetical zinc‐blende MnTe have been grown by molecular beam epitaxy. Epitaxial layers (0.5 μm thick) of MnTe were characterized using x‐ray diffraction and transmission electron microscopy; optical reflectance measurements indicate a band gap of ∼3.2 eV. A series of strained single quantum well structures was fabricated with zinc‐blende MnTe forming the barrier to CdTe quantum well regions; photoluminescence spectra indicate optical transitions corresponding to strong electron and hole confinement.

Molecular beam epitaxy of diluted magnetic semiconductor (Cd1−xMnxTe) superlattices

In this letter we report the first growth of diluted magnetic semiconductor superlattices. Bright and dark field transmission electron microscopy images confirm that the superlattices consist of distinct periodic layers of uniform composition and thickness. The photoluminescence spectra of the superlattices are found to be over three orders of magnitude more intense when compared to uniform thin films (and bulk samples) grown under similar conditions. The reason for this large increase is not clearly understood but this effect may have important consequences for future applications of these novel materials in optoelectronic devices.In this letter we report the first growth of diluted magnetic semiconductor superlattices. Bright and dark field transmission electron microscopy images confirm that the superlattices consist of distinct periodic layers of uniform composition and thickness. The photoluminescence spectra of the superlattices are found to be over three orders of magnitude more intense when compared to uniform thin films (and bulk samples) grown under similar conditions. The reason for this large increase is not clearly understood but this effect may have important consequences for future applications of these novel materials in optoelectronic devices.

Nucleation and characterization of pseudomorphic ZnSe grown on molecular beam epitaxially grown GaAs epilayers

The heteroepitaxial growth of ZnSe on GaAs epilayers grown by molecular beam epitaxy is found to occur via a two‐dimensional growth mechanism. Alternatively, nucleation on a GaAs substrate exhibits three‐dimensional growth characteristics. The differentiation of the type of nucleation is evidenced by reflection high‐energy electron diffraction intensity oscillations, as well as the dynamic behavior of the diffraction patterns. Photoluminescence measurements of pseudomorphic ZnSe epilayers grown on GaAs epilayers provide a direct measurement of ZnSe deformation potentials.

Wide gap II‐VI superlattices of ZnSe‐Zn1−xMnxSe

In this letter we report the first growth of wide gap II‐VI semiconductor superlattices of Zn1−xMnxSe (0<x<0.51). The superlattices are grown by molecular beam epitaxy. Bulk crystals of Zn1−xMnxSe (0<x<0.57) grown in the past have shown a predominance of the zincblende phase only up to x=0.3; above this mole fraction a predominance of the hexagonal phase is observed. For the superlattices and epilayers reported here, only the zincblende phase (100) is present over the entire composition range investigated. Transmission electron microscopy shows clear evidence of the superlattice structure. Photoluminescence measurements of ZnSe epilayers show a dominant free‐exciton feature while the Zn1−xMnxSe epilayers exhibit two distinct photoluminescence peaks. The relative intensities of band‐to‐band transitions and Mn‐related transitions are somewhat comparable for the epilayers. However, the superlattices having ZnSe in the wells show virtually no Mn‐related emission regardless of the mole fraction of Mn in the ba...