| Description |
In recent years the demand for germanium has swiftly increased due to its use in Infrared (IR) optics, gamma-radiation detectors, and in large part to the importance as a substrate for concentrator multijunction celestial and terrestrial based solar cells. Because of the high cost of germanium, and the weight limits of space systems, germanium wafers used in multijunction space solar cells are ultra thin and therefore susceptible to failure due to defects laid in from Czochralski (CZ) crystal growth, and wafer processing. These defects can greatly alter or hinder the electrical properties of the device made from these germanium wafers because of stress, or affect the growth of any material such as gallium arsenide grown epitaxially on the germanium wafer. The ability to locate and measure these defects is critical in developing a growth and wafering process to produce dislocation free germanium crystals and ultrathin wafers cut from them. A chemical etching solution has been found to reveal pits that correspond to dislocations in p-type germanium wafers. The etching solutions, which includes Cu(NO<sub>3<sub>)<sub>2<sub> dissolved in HF & HNO<sub>3<sub> and H<sub>2<sub>O<sub>2<sub> & HNO<sub>3<sub>, are shown to disclose defect points for germanium wafers that were grown off the [100] plane 4<super>°<super>-8<super>°<super> towards the [111] plane to provide multiple and random lattice sites for high quality epitaxial growth. Alterations of the etch solution were also examined in order to develop a chemical polishing technique, which aided the turnaround time of dislocation examination. The morphology of the etched surface was examined with varying etch times. The surface of the etched wafers was observed using a light microscope that possessed Nomarski Differential Interference Contrast (DIC) imaging capability. |
