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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.

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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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We report on magnetic and structural properties of n-and p-type GaN layers implanted with Mn, Cr, and V. The samples were subsequently annealed in a N 2 atmosphere at a constant temperature in the range between 700 and 1050°C. Measurements of the magnetization as a function of magnetic field as well as of the temperature show typical paramagnetic behavior. In addition, a weak antiferromagnetic coupling between the implanted ions was observed. 3d-metal rich precipitates of crystalline nature are revealed by high resolution transmission electron microscopy.

Superconducting Nb–In0.53Ga0.47As/In0.77Ga0.23As/InP–Nb contacts with an electrode separation of 450 nm were fabricated. Due to the high mobility of the two-dimensional electron gas, the current transport can be described within the clean limit regime. At 0.3 K a critical current of 3.8 μA was obtained for 6 μm wide contacts leading to a characteristic voltage of 190 μV. The decrease of the critical current with increasing temperature can be explained by a theory developed by A. Chrestin, T. Matsuyama, and U. Merkt [Phys. Rev. B 49, 498 (1994)], which takes δ-shaped barriers at the superconductor/semiconductor interfaces into account.

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