S. Kaiser et al., Structural properties of AlGaN/GaN heterostructures on Si(111) substrates suitable for high-electron mobility transistors, J VAC SCI B, 18(2), 2000, pp. 733-740
Transmission electron microscopy (TEM) investigations of metal organic vapo
r phase deposition grown AlxGa1 - xN/GaN heterostructures on Si(111) contai
ning an AIN high-temperature buffer layer have been carried out. The struct
ural properties at the interface and in the epilayer as well as the electro
nic properties suitable for a high electron mobility transistor (HEMT) were
analyzed and compared with systems grown on Al2O3(0001). High resolution T
EM (HRTEM) at the AlN/Si(111) interface reveals a 1.5-2.7 nm thick amorphou
s SiNx layer due to the high growth temperature of T-AIN = 1040 degrees C.
Therefore, a grain-like GaN/AlN region extending 40-60 nm appears and it is
subsequently overgrown with (0001) orientated GaN material because of geom
etrical selection. The residual strain at the AlN/Si(111) interface is esti
mated to be epsilon(r) = 0.3+/-0.6% by Fourier filtering of HRTEM images an
d a moire fringe analysis. This indicates almost complete relaxation of the
large mismatch f(AlN/Si)= +23.4% which seems to be supported by the SiNx l
ayer. Weak beam imaging and plan view TEM show typical threading dislocatio
ns in the epilayer with a density of 3x10(9) cm(-2) extending along < 0001
> which sometimes form grain boundaries. An AlxGa1 - xN/GaN interface rough
ness of 3 monolayers is estimated and a small AlxGa1 - xN surface roughness
of 1.5 nm is obtained by HRTEM and atomic force microscopy investigations
which correspond to two-dimensional growth. C-V and Hall measurements revea
l two-dimensional electron gas at the Al32Ga68N/GaN interface that has a sh
eet carrier concentration of 4x10(12) cm(-2). The electron mobility of 820
cm(2)/Vs measured at room temperature is applicable for a HEMT grown on Si(
111). (C) 2000 American Vacuum Society. [S0734-211X(00)06002-9].