A solution of the effective-mass Schrödinger equation in general isotropic and nonparabolic bands for the study of two-dimensional carrier gases Energy band nonparabolicity is present in the majority of materials used in heterojunctions, quantum wells, and superlattices. In the present work we derive a simplified dispersion relation for electrons using the k-p model. We demonstrate that this dispersion relation can account for nonparabolicity in both narrow and wide gap isotropic semiconductors. We then calculate the carrier effective mass and densities of states for both two-and three-dimensional electron systems. Finally, we derive a simple analytical relation between the carrier concentration and the Fermi energy in a nonparabolic two-dimensional electron gas. Agreement with a numerical model is demonstrated, while the traditional, parabolic approximation results in a large error. The simplicity of the new approximation allows an intuitive understanding of the nonparabolicity effect in two-dimensional systems. Therefore, the new approach should be useful for design, characterization, and modeling of quantum semiconductor devices with nonparabolic energy bands. 4382

No abstract

Measurements of the vertical mobility of photo-excited carriers in quantum well infrared detectors are reported. The low temperature mobility is extracted by means of a photo geometrical magnetoresistance technique. This approach is most suitable for the multi quantum well structure geometry. Both rectangular and stepped well structures were studied. They exhibit asymmetry with regard to bias polarity for both gain and mobility. This asymmetry is shown to be contributed by both well structure, and growth induced inequivalent interfaces. The low field mobility is governed mainly by unscreened ionized impurity scattering in the barriers. The well interfaces act as additional anisotropic scattering centers. We observe clear correlation between the extracted drift velocity and the optical gain. It is postulated that anisotropic well recapture causes polarity dependent energy distribution above the barriers. In addition, we conclude that intervalley scattering of the hot electrons has a substantial influence on the detector performance.

Last year SCD presented an un-cooled detector product line based on the high-end VO x microbolometer technology. The first PFA (BIRD384) launched was a 384x288 software configurable (to 320x240 or other) format with 25µm pitch 1 . NETD values for these FPAs are better then 50mK with an F/1 aperture and 60 Hz frame rate. Since then SCD has concentrated in improving both spatial and temporal performance. In order to reduce the Residual Non-Uniformity (RNU) and increase the time span between shutter operations, SCD has incorporated various features within the FPA and supporting algorithms 2 . Improved temporal performance was achieved by optimizing concurrently the membrane structure and ROIC electronics. SCD has demonstrated temporal NETD of ~ 20mK @ F/1 at 30Hz on a 160x120 BIRD compatible array. This figure of merit, accompanied by the superior stability and reduced power consumption, makes SCD's VOx based detectors suitable candidates for a broad range of "high-end" military and commercial applications.

SCD has established an uncooled detector product line based on the high-end VO x µ-bolometer technology. The first PFA launched was BIRD384, a 384x288 (or 320x240) configurable format with 25µm pitch. Typical NETD values for these FPAs are below 50mK with an F/1 aperture and 60 Hz frame rate. The product exhibits superior image uniformity, stability and reduced power consumption, making it most suitable for a broad range of "high-end" military and commercial applications. In this paper we report on our progress in development of new products in accordance with SCD's uncooled products roadmap: 1. A "sensitive" version of BIRD384 with an improved NETD of ~ 30mK @ F/1, 60Hz frame rate. This performance is achieved by optimizing concurrently the membrane structure, pixel architecture and ROIC electronics. 2. An improved version of BIRD384 ROIC that supports 100/120Hz frame rate and high dynamic range ("Fire Man" option). 3. First data of the BIRD640 -a 640x480 array with 25µm pitch and NETD ≤ 50mK @ F/1, 60Hz frame rate.