Selective area metalorganic vapor phase epitaxy growth of prism-shaped GaAs resonators for folded cavity surface emitting lasers

Abstract

Selective area (SA) metalorganic vapor phase epitaxy (MOVPE) proves to be an effective method of manufacturing nonplanar structures with precisely controlled sizes and orientations of their facets. Excellent flatness of the facets makes SA MOVPE especially useful for optoelectronic applications such as microcavities. In this work we use this technique to grow prism-shaped GaAs cavities for novel prismatic (folded) cavity surface emitting laser diodes. Design of these devices has been recently proposed. Critical points in growing the cavities are: (i) to ensure 90° angle at the top of the prism, (ii) to obtain flat walls of the GaAs prism (4 μm wide at the base) with the sharp top, (iii) to avoid an excessive number of polycrystalline precipitates on the surface of a dielectric mask (SiO 2 100 nm thick) despite the very disadvantageous ratio of openings to whole substrate area. Growth-rate calculations have been performed using total area of mask openings as an active substrate surface. For proper prism growth the pulsing epitaxy technique using Aixtron MOVPE LP system was applied, where interruption growth periods which enabled efficient surface molecules migration into openings. Optimization of the growth/interruption time versus partial pressure of gallium was essential for laser application to obtain suitable shape of the prisms. The best results for 2 μm high prisms were obtained for 272 pulses of 2 s growth/3 s interruption, when total pressure and temperature were 100 mbar and 700°C, respectively.