Effects of the MBE growth temperature on Si-doped AlxGa1-xAs (x=0, 0.26) and HEMT
The effects of the growth temperature on photoluminescence (PL) as well as the net donor concentration have been studied concerning heavily Si-doped GaAs and Al0.26Ga0.74As grown by molecular beam epitaxy (MBE). Attention is especially paid to the PL band related to donor-vacancy complexes (SiIII-VIII), i.e. the so-called self-activated (SA) centres. The SA luminescence intensity normalized by the band-to-band emission intensity, which can be regarded as being a characteristic of the SA centre concentration, is found to be minimum at a growth temperature of 650 degrees C in both GaAs and Al0.26Ga0.74As; the normalized intensity in Al0.26Ga0.74As, however, is always about 40 times stronger than that in GaAs grown at the same temperature. While the net donor concentration in GaAs is independent of the growth temperature, that in Al0.26Ga0.74As is found to be maximum at 650 degrees C. Furthermore, a high-electron-mobility transistor (HEMT) fabricated on an MBE-grown N-Al0.26Ga0.74As/GaAs structure exhibits maximum performance when the structure is grown at that optimum temperature of 650 degrees C. The authors propose a model in which the growth temperature dependence of the vacancy (VIII) concentration, which is supposed to have the minimum at 650 degrees C, is the cause of the change in the HEMT performance, as well as that in the net donor concentration in Al0.26Ga0.74As. The growth-temperature dependence of the vacancy concentration is explained in terms of a thermodynamical mechanism in the low-temperature range ( 650 degrees C).