The objective of this work was to investigate the distribution of donor-like centres produced by boron implantation into p-type, Bridgeman grown Hg[0.8]Cd[0.2]Te and fabricate photodiodes from implanted substrates. Low carrier concentration substrates, 4-5x10[16]cm[-3], were implanted at room temperature with dose rates (&phis;) of 4x10[-2] or 6x10[-3]muAcm[-2], to a total dose of 1 x 10[15]B[+] cm[-2] (50,100keV) or 1x10[14]B[+]cm[-2] (150keV), respectively. Encapsulated specimens were annealed at 200°C or 235°C to activate the dopant or redistribute electrically active radiation damage centres to produce p-n junctions. The effects of materials processing on Hg[l-x]Cd[x]Te was investigated by x-ray photoelectron spectroscopy. Concentration profiles of electrically active centres were obtained from differential measurements of the Hall effect and resistivity at 77K. Through a comparison of distributions in as-implanted and annealed samples, the nature of donor-like centres forming the distributions were established. The quality of photodiodes produced from identical samples was assessed through current-voltage, capacitance-voltage and optoelectronic measurements. The nature and distribution of donor-like centres are dependent upon the dose rate of boron ions. An immobile defect is contained within the implanted region. Mercury interstitials (Hg[int]) are complexed within the implanted region for &phis; > 4x10[-2] muAcm[-2]. Irradiation enhanced diffusion of Hg[int] occurs if &phis; < 6x10[-3] muAcm[-2]. Thermal annealing redistributes bound and unbound accompanied by recombination with mercury vacancies and the formation of electrically neutral complexes. Annealing at 235°C for 10 mins completely removes the donor-like activity ascribed to Hg's [int] and reduces the concentration of electrically active immobile defects. P-N junctions are formed between the mercury vacancy distribution and unbound Hg's[int] or the immobile damage centres in annealed substrates. Junction formation is inhibited by the formation of the bound Hg[int] complex. Optimum R[o]A[j] products may be obtained from junctions formed from the immobile defect centre, although degradation of the implanted region occurs after annealing at 235°C. Anodic oxides grow by the differential electromigration of ions, which can produce a passivating layer to further anodization. The native oxide on Hg[0.8] Cd[0.2] Te is an ill-defined chemical mixture of the primary elements (Cd, Hg, Te). Native oxides degrade the R[o]A product of p-n junctions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:378204 |
| Date | January 1986 |
| Creators | Pitcher, P. G. |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/847907/ |
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