Germanium far infrared blocked impurity band detectors.

摘要

Several important issues in the fabrication and performance of Ge Blocked Impurity Band (BIB) devices based on Liquid Phase Epitaxy (LPE) grown Ge films and on ion implantation have been studied and are presented in this thesis.; Growth of high purity Ge films (as required for the blocking layer of a BIB device) by LPE is found to be limited by the P impurities present in the Pb solvent. Purification of Ph has been performed by zone refining using simultaneous RE heating and water cooling in a double walled quartz boat designed and fabricated especially for this work. Films grown from the zone refined Pb have shown an improvement of ∼50x in purity over films' grown with commercially obtained Pb. The impurity concentration has been reduced to ∼1x1014 cm-1, but this is still an order of magnitude higher than needed for the blocking layer of an efficient BIB detector. In addition, the purification of Pb by zone refining has led to the first-ever estimate of the effective segregation coefficient of P in Pb, which is found to be between 0.9 and 0.95.; The growth of Sb doped LPE Ge films with donor concentrations below the metal-insulator transition (as required for the IR absorbing layer of a BIB device) has also been performed. In order to resolve the problem of Sb diffusion into the substrate at the typical starting growth temperature of 650°C, film growth at lower temperatures has been attempted. Films grown at 550°C do not exhibit Sb diffusion into the substrate, but they are only ∼10mum thick, even though enough Ge is present in the melt to grow thicker films according to equilibrium solubility data. Since the absorbing layer of a BIB device should be thick for efficient absorption of radiation, a number of experiments have been performed to grow thicker films at 550°C. Growth runs have been performed using larger amounts of solvent, slower cooling rates, and longer growth times, but the films obtained were only slightly thicker than 10mum. It is believed that the reason for the discrepancy in theoretical vs. experimental film thicknesses could be the limitation of solute diffusion during growth.; BIB devices have been fabricated by growing Sb doped Ge epilayers on high purity n-type Ge substrates, and subsequently polishing back the substrates to form the blocking layer. These devices exhibit good blocking characteristics with low dark currents, and the spectral response extends to longer wavelengths than Ge:Sb photoconductors. The optical response of these devices is severely limited by the diffusion of Sb at the absorbing layer - blocking layer interface and the inability to grow the blocking layer epitaxially.; A new type of BIB device has been fabricated, wherein the necessary doped layers are created using ion-implantation of B into high-purity Ge. These Ge:B implant BIBs exhibit excellent blocking characteristics and low dark current just like their LPE based counterparts. In addition, the spectral response extends to ∼45 cm-1, clearly showing the formation of an impurity band.