Two-dimensional electron gases in Ga-face and N-face AlGaN/GaN heterostructures grown by plasma-induced molecular beam epitaxy and metalorganic chemical vapor deposition on sapphire
R. Dimitrov et al., Two-dimensional electron gases in Ga-face and N-face AlGaN/GaN heterostructures grown by plasma-induced molecular beam epitaxy and metalorganic chemical vapor deposition on sapphire, J APPL PHYS, 87(7), 2000, pp. 3375-3380
We report on the growth of nominally undoped GaN/AlxGa1-xN/GaN (x < 0.4) hi
gh mobility heterostructures with N-face or Ga-face polarity on sapphire su
bstrates by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic
chemical vapor deposition in order to study the formation and electrical tr
ansport properties of polarization induced two-dimensional electron gases (
2DEGs). By depositing a thin AlN nucleation layer on the sapphire substrate
s before the growth of a GaN buffer layer by PIMBE, we were able to change
the polarity of the wurtzite films from N to Ga face. The switch in the pol
arity causes a change in the sign of the spontaneous and piezoelectric pola
rization directed along the c axis of the strained AlGaN barrier. As a cons
equence the polarization induced 2DEG is confined at different interfaces i
n heterostructures with different polarities. The transport properties of t
he 2DEGs in Ga- and N-face heterostructures were investigated by a combinat
ion of capacitance-voltage profiling, Hall effect, and Shubnikov-de Haas me
asurements. Dominant electron scattering mechanisms are studied in order to
provide the knowledge necessary for further improvements of the electron t
ransport properties and performance of AlGaN/GaN based "normal" (based on G
a-face heterostructures) and "inverted" (based on N-face heterostructures)
high electron mobility transistors. (C) 2000 American Institute of Physics.
[S0021-8979(00)03007-3].