Reversible Electrical-Properties of LEC GaAs

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Conference Proceeding

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Undoped, low-pressure, liquid-encapsulated Czochralski GaAs can be reversibly changed from semi-insulating (P ~ 1.8 x 107fl -cm, ~ ~ 6.3 x 10~ cm2/V- Sec, n = 5.6 x 107 cm 3) to conducting (P ~ 2,2. fl -cm, ,a = 7.1 x 103 cm2 / V- Sec, n 4,0 x 10" cm a) by a purely thermal process. The above results correspond to the fifth and sixth cycles, respectively, of this process. We have performed temperature-dependent Hall effect (TDH), photoluminescence, IR absorption, spark-source mass spectroscopy, secondary ion mass spectroscopy, and optical stress analysis, on these samples. In this paper we will mainly be concerned with the TDH results for the conductive state, which give a dominant donor energy (E~) and concentration (N~} of 0.13eV and 6,9 x 10'~ cm ~, respectively, and a net shallow acceptor concentration (N,s - Nos) of 6.3 x 10~cm 3, Thus, N,s > 6 x 10'~ cm ~, which is much larger than the carbon concentration ( - 7 x 10`4 cm ~) and any other impurity except boron ( - 8 x 10'" cm ~). The same statement holds true for No. Thus, along with EL2 the system is dominated by defects. By comparing with a very similar center produced by 1 MeV electron irradiation we believe that the 0.13eV level is related to the As vacancy or interstitial. The change in the concentration of this defect under the thermal treatment is then likely due to the motion of As. It should be noted that the concentration of the deep donor, EL2, which controls the semi-insulating state (Era, ~ 0.78eV), is nearly constant in these samples at about 1.1 x 10`6cm '. However, because of the close compensation ( > 90 %), a small change ( - 1 x 10~Scm ~) in any donor or acceptor concentration is sufficient to swing the conductivity from conducting to semi-insulating or vice versa. Models for the conversion will be discussed. It is clear that the thermal process involved here has high technological importance.


This paper was presented at the 28th Annual Electronic Materials Conference, June 25-27, 1986 in Amherst, MA.