Liquid Phase Epitaxy Centrifuge for Growth of Ultra-pure Gallium Arsenide for Far Infrared Photoconductors

摘要

Gallium arsenide extrinsic photoconductive detectors offer an extended spectral response in the far infrared (FIR) compared to presently available photodetectors, with the possibility of wavelength coverage from 60 to 300μm. They can also be made in large planar structures, making them attractive for various far-infrared astronomical applications. In the past, continuous progress in material research has led to the production of pure, lightly and heavily doped n-type GaAs layers using liquid phase epitaxy (LPE). Sample detectors demonstrated the expected infrared characteristics of bulk type devices. Considerable improvement of detector performance could be expected from development of blocked impurity band (BIB) devices. These multi-structured detector types provide enhanced IR absorption and sensitivity due to the attainable higher doping of the infrared sensitive layer. However, the dark current in BIB detectors is determined by the level of unintentional majority doping for the relatively thin blocking layer, thus requiring ultra-high purity GaAs. With a new technique, using centrifugal forces for the LPE material growth, we intend to achieve this goal. Recently, such a growth facility has become operational at UC Berkeley. Outside contamination during the LPE growth process is largely reduced by a suspension of the crucible on active magnetic bearings in a completely closed environment. A sequential combination of centrifugal and gravitational forces provides the proper transport of the Ga solution in the growth crucible. Technical details of this unique equipment and first results of the initial growth runs will be reported.