Localized Epitaxy of GaN by HVPE on patterned Substrates
- PDF / 954,615 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 335 Views
Internet Journal Nitride Semiconductor Research
Localized Epitaxy of GaN by HVPE on patterned Substrates O. Parillaud1, V. Wagner1, H. J. Buehlmann1 and Marc ILEGEMS 1 1Institut
de Micro- et Optoélectronique, Ecole Polytechnique Fédérale de Lausanne,
(Received Monday, June 22, 1998; accepted Monday, October 19, 1998)
We report ongoing experiments on the growth of GaN by hydride vapor phase epitaxy (HVPE), using a newly designed Aixtron horizontal reactor. Growth was carried out on c-plane Al2O3 substrates on which a thin GaN layer had been predeposited by MOVPE and patterned using a dielectric mask. The mask pattern was designed to give information on the growth rate and morphology along different directions, and contained both a star-shaped pattern and arrays of parallel stripes of various widths and orientations. All growths were performed at atmospheric pressure and ~1050°C deposition temperature. For the range of experimental conditions investigated the maximum ratios of lateral to vertical growth velocities of around 2 and coalescence of the layer after approximately 10 µm of growth were observed for stripes oriented along the 〈1100〉 direction.
1
Introduction
One of the key problems remaining in the growth of GaN and (Al,Ga,In)N mixed crystals is the lack of an appropriate substrate. One of the solutions proposed consists of the realization of self supported GaN layers grown by Hydride Vapor Phase Epitaxy to be used as pseudo-homoepitaxial substrates [1]. More recently, the use of the Epitaxial Lateral Overgrowth (ELOG) technique has been shown to be effective for the reduction of dislocation densities of GaN grown on sapphire by several orders of magnitude [2]. The combination of HVPE growth with the ELOG technique thus appears as the most promising approach to high crystalline quality. Hydride VPE has already been used successfully for selective epitaxy of other III/V compounds as GaAs [3] or InP [4]. The high selectivity and large growth rate anisotropy which are typical features of HVPE clearly make this method very suitable for such a growth on partially masked substrates [5], [6], [7]. 2
Experimental
The growth experiments were performed in a newly designed horizontal AIXTRON reactor. A schematic drawing of the reaction chamber heated by a 5 zones furnace is presented in Figure 1. A single two inch wafer can be loaded on the substrate holder which is gas foil rotated. Gallium chloride is synthesized by the reaction of HCl flowing over metallic gallium at high temperature and is transported separately from NH3 in different
quartz tubes to the deposition zone where the two species are mixed. All experiments were performed at atmospheric pressure with nitrogen as carrier gas. The flow rate for ammonia was maintained at 1.2 l/min. while the HCl flow over Ga was varied from 10 to 40 cc/min. The total flow in the reactor was kept constant at 6 l/min. Source temperature and deposition temperature were 850 °C and 1050 °C respectively. By varying the GaCl partial pressure, growth rates from 10 to 50 µm/
Data Loading...
