Abstract. We present a study of the sources of strain in GaN heteroepitaxy by in-and ex-situ measurement techniques. With an in-situ curvature measurement technique the strain development can be directly correlated to the different layers and doping in simple and device structures. We show several solutions for strain reduction and control. High-quality devices grown on Si are demonstrated.Despite its great commercial success for the mass production of blue and green light-emitting diodes the epitaxial growth of GaN is stiH hindered by the lack of homosubstrates. Thus epitaxial growth is commonly performed on heterosubstrates as sapphire, SiC or Si. These substrates all have a large lattice (3.5-17%) and thermal (-25-116%) mismatch leading to di:fficulties in heteroepitaxial growth and are a high number of threading dislocations for all substrates and cracking for layers exceeding 1 and 3 11-m on Si and SiC, respectively. Especially the latter problem hindered GaN device layer growth on Silicon until the late 90 s. After first reports on cracked, but functioning LED structures on Si [1,2] grown by molecular beam epitaxy (MBE) several methods to reduce cracking and devices were presented [3,4,5,6,7]. It turned out that strain engineering was crucial for the successful growth of device structures on Si. Here, we present a study on the sources of strains and stresses in GaN heteroepitaxy, which is not only valid for the growth on silicon, but also on other heterosubstrates as sapphire and SiC.
GaN devices on Si are interesting for low-cost, high-power devices as LEDs and FETs. Until recently, most LED and FET devices suffered from cracking and low output power and additionally, from high series resistances for vertically contacted LEDs. Here, we give a brief overview on state of the art crackfree, bright LEDs with an output power up to 0.42 mW and AlGaN/GaN FETs with an output power of 2.5 W/mm at 2 GHz.
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