Ay. Polyakov et al., ON THE ORIGIN OF ELECTRICALLY ACTIVE DEFECTS IN ALGAN ALLOYS GROWN BYORGANOMETALLIC VAPOR-PHASE EPITAXY, Journal of applied physics, 80(11), 1996, pp. 6349-6354
Shallow and deep centers were studied by means of temperature dependen
t Hall effect and photoluminescence (PL) measurements in two sets of u
ndoped n-AlGaN samples grown by organometallic vapor phase epitaxy. Th
e samples of these two series were grown under different conditions an
d had, as a result, electron concentrations differing by several order
s of magnitude. The composition dependence of ionization energies of d
ominant donors in these two sets of samples is very different indicati
ng that different types of centers are involved, but in both cases the
y are most probably related to some native defects. These defects beha
ve as hydrogen-like donors for low Al compositions and become increasi
ngly deeper with increasing Al content. The shallow-deep transition oc
curs at about x=0.2 in the low conductivity AlxGa1-xN series and at ab
out x=0.5 for the high conductivity series. Several PL bands were dete
cted in AlGaN and it is shown that the band at 3.05 eV is due to a rad
iative transition between deep donors in the upper part of the band ga
p and holes in the valence band or on shallow accepters. For the yello
w luminescence band at 2.25 eV it is demonstrated that this band consi
sts of two overlapping bands and that the dominant band is due to a tr
ansition between the native donors and a carbon-related deep center. (
C) 1996 American Institute of Physics.