Defect-Impurity Interaction in Irradiated n-GaAs
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DEFECT-IIMPURITY INTERACTION IN IRRADIATED n-GaAs F.P. K1DRHUNDV, T.A. PRDIKHRMO, N.A. SOBOLEV, and E.A. KUDRIAVI'SEA Institute of Solid State and Semiconductor Physics, 220072 Minsk, ul. P. Brovki 17, Rep. of Belarus
ABSTRACT The creation of radiation defects (RDYs) and their interaction with shallow impurities in 3-4 MeV electron irradiated n-GaAs have been studied by means of photoluminescence (PL) and Hall effect. The irradiations were carried out at sample temperatures ranging from Ti = 30 to 500-C. It has been found for the first time that for high fluences at roan temperature the shallow donor concentration starts to decrease. The behaviour of the carrier concentration (n), mobility 9.1) and of the concentrations of the shallow acceptors C(As) and Ge(As) has been studied on irradiation and annealing. It was found that the behaviour of the As vacancy govern the main annealing processes observed.
IN'TRDUCTION It is generally accepted that in GaAs irradiated with electrons at and below roan temperature intrinsic RD's are formed which do not interact with shallow chemical donors [1, 2]. On the contrary, carbon acceptors C(As) and isovalent boron impurities B(Ga) do form complexes with intrinsic RD's giving rise to local modes in the IR absorption spectra [3-5]. In the course of subsequent annealing an interaction of RD's with other impurities including donors (e.g. Si(Ga) (6]) Was observed. The main doping impurities in neutron transmutation doped (NTD) GaAs are Se and Ge [7]. Whereas Se in GaAs is always a donor, the electrical behaviour of Ge depends on which sublattice site, Ga or As, the atoms are localised. In addition, other technological rest impurities such as C, B, 0 are present in as-grown crystals. In this paper we report PL and Hall effect measurements an n-GaAs irradiated with 3-4 MeV electrons at temperatures from 30 to 500CC and sub-
jected to subsequent thermal annealing. The behaviour of shallow donors and of
C(As) and Ge(As) acceptors is monitored and compared with the changes electrical parameters of the crystals.
in
the
EXPERIMEVTAL Two kinds of samples were used. The first one was relatively pure VPE grown n-GaAs with the net carrier concentration n(300 K) 1 1El4 cm-3. The second one was bulk NTD GaAs fabricated in the following way. Nominally 300 undoped LEC grown n-GaAs with n(300 K) = (1-2)E16 cm-3, r( K) = 5E3 an2/(V. s) and ccompensation ratio K = 0.5 was subjected to neutron irradiation and subsequent annealing at 900oC for 20 min under equlibrium As vapour pressure to achieve n(300 K) = IE17 cm-3 and pu( 3 0 0 K) = 5E3 cm2/(V. s). As deduced frnm PL spectra of the starting crystal the main shallow acceptor in it was C(As). From the ccmpensation ratio and carrier concentration we estimate the C(As) concentration not to exceed 2E16 am-3. PL was excited with an Arion laser, dispersed through a grating monochrcmator and detected by a cooled photamultiplier with a S-1 cathode. All PL measurements were made in liquid He at 4.2 K. The irradiation with 3-4 MeV electrons was performed a
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