AlGaN/GaN MODFET regrown by rf-MBE on MOCVD templates
2007
AlGaN/GaN devices are typically grown on foreign substrates such as SiC and sapphire due to lack of commercial
bulk GaN. Metalorganic chemical vapor deposition (MOCVD) is a widely used method for growth of GaN templates
for these structures even for other growth methods. Because the growth temperature during molecular beam epitaxy
(MBE) is low, dislocation motion is hindered leading to a high dislocation density, particularly pure edge type, when
grown directly on foreign substrates. On the other hand, low background doping, sharp interface and well-controlled
growth rate allow MBE to grow high performance modulation doped field effect transistor (MODFET) structures on
MOCVD GaN templates. However, the regrowth interface in this case has been reported to act as a parallel channel
unless Zn-doped GaN templates were used. [ J. Appl. Phys. v92 p338 ] In this paper we report on the control of the
regrowth interface of GaN/AlGaN MODFETs by rf-assisted MBE on GaN templates prepared by MOCVD. We have
found that the defective parallel channel at the regrowth interface could be effectively eliminated by a proper growth
procedure and pre-cleaning using KOH combined with high temperature (800 o C) thermal annealing in vacuum.
Reflection high energy electron diffraction (RHEED) was used to monitor the interface quality to a first order during
the initial growth stages. Electrical and structural properties at the regrowth interface were analyzed by capacitance-voltage
(CV) measurements and transmission electron microscopy (TEM). Al 0.3 Ga 0.7 N/GaN MODFET structures
grown under the optimized conditions exhibited a maximum transconductance of 230 mA/mm for a 1mm gate length.
Keywords:
- Metalorganic vapour phase epitaxy
- Chemical vapor deposition
- Doping
- Molecular beam epitaxy
- Gallium nitride
- Analytical chemistry
- Electronic engineering
- Field-effect transistor
- High-electron-mobility transistor
- Materials science
- Reflection high-energy electron diffraction
- Sapphire
- Optoelectronics
- Aluminium nitride
- Electrical engineering
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