We present results of optical degradation experiments on blue-green ZnSe-based diode laser structures. A micro-focused wavelength selectable laser is used for degradation and the luminescence from the degrading region is simultaneously recorded. The degradation speed at a given optical power density depends strongly on the doping of the structure and on the photon energy: undoped structures do not degrade, while the threshold photon energy to induce degradation depends on the degree of compensation in the p-doped layers. However, at high photon energies, an improvement in compensation does not slow down the degradation process, leading to the suggestion that the nitrogen acceptor itself is unstable under these conditions.

No abstract

The surface structure of molecular beam epitaxially grown HgTe(001) has been studied under in situ ultrahigh vacuum conditions. The as-grown samples were investigated by means of x-ray photoelectron spectroscopy (XPS), spot profile analysis of low-energy electron diffraction, reflection of high-energy electron diffraction and scanning tunneling microscopy (STM). They exhibited a c(2×2) surface reconstruction with an additional weak (2×1) component in both diffraction experiments. The surface was shown by XPS to be terminated with Hg atoms. In addition, by means of STM experiments, we have been able to resolve the atomic structure of the reconstructed surface and to detect domain boundaries along the [11̄0] direction whose local symmetry is twofold and, therefore, the probable cause of the weak (2×1) reconstruction.

An image plate has been used as a detector for high‐resolution X‐ray diffraction of semiconductor heterostructures. A series of 2θ intensity distributions is recorded for different rocking angles ω for the sample and subsequently transformed to a reciprocal‐space map. Maps of symmetric and asymmetric reflections of two samples are presented. A reduction in measurement time by a factor of 36 was achieved by recording information simultaneously along 2θ on the image plate compared to conventional measurement with a scintillation counter. Favourable results were obtained with broad reflections from samples with low structural quality and asymmetric reflections in the grazing exit geometry.

We have fabricated II–VI wide gap hetero PIN photodiodes made of ZnMgSSe with excellent structural and interface quality and with a high external quantum efficiency of about 60%, which is close to the theoretical limit. The internal quantum efficiency reaches peak values of more than 80%. The onset of the sensitivity is very sharp, leading to a quantum efficiency less than 10−4 at wavelength 60 nm below the band gap. Using the wide range of energy gaps from 2.68 to 3.1 eV, it is possible to fabricate wavelength selective detectors if the energy gap of the top p-type layer is chosen slightly higher than that of the intrinsic zone. The dark current is below 0.1 pA/mm2. In the low signal limit, the noise equivalent power can be estimated to be below 10−15 WHz/mm2 at the peak external quantum efficiency, surpassing ultraviolet optimized Si detectors.