HgCdTe MBE Technology: A Focus on Chemical Doping
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HgCdTe MBE Technology : A Focus On Chemical Doping Owen K. Wu, Hughes Research Laboratories, 3011 Malibu Canyon Road, Malibu, CA 90265
ABSTRACT HgCdTe MBE technology is becoming a mature growth technology for infrared focal plane array applications. The ability to dope HgCdTe with In(n-type) and As(p-type) dopants in-situ provides greater flexibilities for fabricating heterojunction devices. In this paper, we will first discuss the current status of HgCdTe MBE growth and then focus on the key results in the control of In(n-type) doping, various approaches and breakthroughs in the growth of As(p-type) doped HgCdTe and issues related to doping such as memory effects and dopants activation. In addition, device results from double layer heterojunction structure(DLHJ) will be briefly discussed.
INTRODUCTION It is well known that II-VI compound semiconductors have numerous existing and potential applications in the optoelectronics. For instance, in the wide band gap arena that ZnSe has a band gap of nearly 2.67 eV at room temperature and is an ideal material for blue light emitting diode and laser applications.(ref.1) In the narrow band gap arena, HgCdTe has thus far received the greatest development effort and found the largest market for infrared detectors.(ref.2) MBE researchers have devoted their efforts over the last decade to make artifically layer structures such as quantum well and superlattices for fabricating advanced optoelectronic devices.(ref.3-5) However, the major technology hurdles in the MBE growth of II-VI compound semiconductors have been the difficulties in making n-type and ptype materials in-situ, especially low resistivity p-type II-VI materials are particularly uneasy to grow by MBE. The problem in making p-type II-VI materials for both wide(e.g. ZnSe) and narrow band gap(e.g. HgCdTe) materials is quite similar that is due to the vacancies and self-compensation effect.(ref.6&7) Recently, major breakthroughs have been achieved in growing p-type ZnSe by nitrogen(ref.8&9) and p-type HgCdTe by arsenic in a number of laboratories.(ref.10-12) Table 1 lists the common dopants used for the growth of n-type and p-type II-VI semiconductors. In this paper, we will focus on the I1-VI narrow bandgap HgCdTe semiconductors, first summarizing the status of HgCdTe MBE growth, then discussing key results on the control of n-type doping with indium, and Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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describing various approaches and results of growing p-type HgCdTe with arsenic. In addition, issues relating to memory effects and the efficiency of the dopants activation will be disscused. Finally, diode results from MBE grown double layer heterojunction(DLHJ) structures will be discussed. EXPERIMENTAL The MBE system which we use to grow HgCdTe samples is a modified V80H MBE system manufactured by Vacuum Generators, a division of Fison Instruments. This system has two interconnected V-80H growth chambers with integrated surface analysis and ion etching capabilities. Each growth chamber
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