METASTABLE DEFECTS IN AS-GROWN AND ELECTRON-IRRADIATED AL0.3GA0.7AS

New metastable defects have been observed in Si-doped Al0.3Ga0.7As lay ers, grown by MOCVD and irradiated with 1 MeV electrons in the dose ra nge 3 x 10(14)-3 x 10(16) cm(-2) at T = 300 K. The investigations have been carried out by DLTS after preliminary isochronous and isothermal annealing with applied reverse bias voltage and at U = 0. In as-grown AlGaAs the stable-state parameters with a thermal activation energy E 1(g) = E(c) - 0.17 eV and electron capture cross section sigma(n) = 1. 1 x 10(-13) cm(2) were identical to those of the E1 defect formed unde r irradiation of AlGaAs and identified as V-As. The parameters of the metastable state were E2(g) = E(c) - 0.21 eV and sigma(n) = 2.5 x 10(- 14) cm(2). The kinetics of configurational transformations of the defe ct was first-order. The thermal activation energy E(a) and the pre-exp onential factor R(0) were 0.39 +/- 0.01 eV and (1.0 +/- 0.3) x 10(11) s(-1) for the defect transition E1(g) --> E2(g) and 0.23 +/- 0.01 eV a nd (3.4 +/- 0.7) x 10(7) s(-1) for the reverse transformation. The met astable defect is supposed to include V-As and, possibly, a donor impu rity. In irradiated material a rise in the concentration of metastable defects has been observed. As in as-grown AlGaAs, the signature of th e stable state was identical to that of the E1 defect, but the transfo rmation mechanism was changed, which is probably connected with the fo rmation of another pair V-As-As-i. The value of R(0) may correspond in order of magnitude to an interstitial As-i single-jump process.