Growth kinetics and characterizations of gallium nitride thin films by remote PECVD
- PDF / 3,135,702 Bytes
- 8 Pages / 576 x 792 pts Page_size
- 60 Downloads / 226 Views
K. J. Bachmann Department of Materials Science and Engineering and Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695
G. Lucovsky Department of Materials Science and Engineering and Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (Received 17 April 1992; accepted 9 December 1992)
Thin films of GaN have been deposited at relatively low growth temperatures by remote plasma-enhanced chemical-vapor deposition (RPECVD), using a plasma excited NH 3 , and trimethylgallium (TMG), injected downstream from the plasma. The activation energy for GaN growth has been tentatively assigned to the dissociation of NH groups as the primary N-atom precursors in the surface reaction with adsorbed TMG, or TMG fragments. At high He flow rates, an abrupt increase in the growth rate is observed and corresponds to a change in the reaction mechanism attributed to the formation of atomic N. X-ray diffraction reveals an increased tendency to ordered growth in the (0001) direction with increasing growth temperature, He flow rate, and rf plasma power. Infrared spectra show the fundamental lattice mode of GaN at 530 cm"1 without evidence for vibrational modes of hydrocarbon groups.
I. INTRODUCTION Gallium nitride (GaN) has been considered as a promising material for optoelectronic applications such as visible and near UV light-emitting diodes (LED's) and blue semiconductor lasers since it has a room temperature direct band gap of 3.4 eV.1 GaN has been proposed as a candidate material for high frequency and microwave power devices due to its high value for the saturated electron drift velocity2 and also as a material for electroluminescence applications.3"5 In addition, the piezoelectric properties and high acoustic velocities of this material make it attractive for acoustic devices.6 Films of GaN have been grown by several different techniques: reactive sputtering,7 CVD (including both low- and high-pressure approaches),8'9 MOCVD, 1011 PECVD, 12 reactive ion beam deposition,13 and molecular beam epitaxy (MBE).14'15 Various substrates, including silicon, silicon carbide, magnesium oxide, zinc oxide, GaAs, and sapphire, have been used for film deposition. Conventional CVD has been the most commonly used method to grow GaN, using GaCl and NH 3 as the respective Ga- and N-atom source gases. The substrate temperatures for this process are typically 900-1150 °C. MOCVD permits a reduction of the substrate temperature to 700-800 °C for heteroepitaxial J. Mater. Res., Vol. 8, No. 4, Apr 1993
growth of GaN. GaN films deposited below 700 °C are generally polycrystalline. Direct PECVD has been used to activate either N 2 or NH 3 as N-atom sources. Thus far, GaN films grown by advanced CVD techniques, such as MOCVD or PECVD, are not superior to those grown by conventional, high-temperature CVD in terms of low carrier concentration and/or epitaxial quality. For example, the net ionized donor concentrations in such films are typically in the range of 1018 to 1020 cm 3 , pr
Data Loading...
