Wide GaN Stripes by Lateral Growth in Metalorganic Vapor Phase Epitaxy
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•Optoelectronics and High Frequency Device Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305, JAPAN, [email protected] **Fundamental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305, JAPAN ABSTRACT We investigated the growth conditions for enhancing epitaxial lateral overgrowth (ELO) of GaN stripes selectively grown by low-pressure metalorganic vapor phase epitaxy. The ELO was enhanced for GaN stripes and with a small trimethylgallium flow-rate. This tendency did not depend on mask materials. The cross-sectional shape of the GaN stripes was trapezoidal for SiO2 masks, and rectangular for silicon nitride (SiN,) masks in a certain growth condition. A low dislocation density in the ELO region was obtained not only for the SiO2 masks but also for the SiN, masks. INTRODUCTION Selective growth and epitaxial lateral overgrowth (ELO) of GaN are drawing attention. These techniques have been applied to the fabrication of quantum dots and wires [1] and GaN
substrates with a low dislocation density [2][3][4]. The fabrication of GaN-based laser diode (LD) structures is another possible application of the ELO. For example, GaN-based LDs with laterally-overgrown ridge-geometry are expected to have wider p-electrodes and lower p-contact
resistance than conventional GaN-based LDs with dry-etched ridge-geometry [5].
For this
purpose, it is important to enhance the ELO in the selective growth of GaN. In this paper, we report the growth conditions for enhancing the ELO of GaN stripes selectively grown with SiO 2 and silicon nitride (SiN,) masks. We also discuss dislocations in the GaN layers selectively grown with these masks. EXPERIMENT The selective growth of GaN was carried out on 1.0-jnm- to 1.5-jim-thick GaN layers grown on sapphire C-face substrates. SiO 2 masks (3000-A-thick) and SiN, masks (2000-Athick) were used. The SiO 2 and the SiNX were deposited using a thermal chemical vapor deposition (CVD) reactor and a plasma CVD reactor, respectively.
These masks were patterned
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Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
to form 2-pm-wide stripe windows in the and the directions of GaN using conventional photolithography and wet etching. The mask pattern had a small coverage ratio of 13% to suppress growth-rate enhancement. In selective growth, a low-pressure metalorganic vapor phase epitaxy (MOVPE) reactor operated at 100 Torr was used. Hydrogen was used as a
carrier gas, and trimethylgallium (TMGa) and ammonia (NH3) were used as source gases.
The
flow-rates were 29, 58, and 116 junol/min for TMGa and 0.18 mol/min for NH 3. These flowrates resulted in the V/III ratios of 6000, 3000, and 1500, respectively. The growth time was 120, 60, and 30 minutes, respectively. The substrate temperature during the selective growth was maintained at 10501C. RESULTS Figure 1 shows scanning electron microscope (SEM) images of GaN stripes selectively grown with SiO 2 and SiNX masks at a TMGa flow-rate of 58 pmnol/min. The stripes had trapezoidal cr
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