MOVPE homoepitaxy of high-quality GaN: Crystal growth and devices

Epitaxial growth on GaN bulk single crystal substrates sets new standards i n GaN material quality. The outstanding properties provide insights into fu ndamental material parameters (e.g. lattice constants, exciton binding ener gies, etc.) with a precision not obtainable from heteroepitaxial growth on sapphire or SiC. With metalorganic vapor phase epitaxy (MOVPE) we realized unstrained GaN layers with dislocation densities about six orders of magnit ude lower than in heteroepitaxy. By the use of dry etching techniques for s urface preparation, an important improvement of crystal quality is achieved . Those layers reveal an exceptional optical quality as determined by a red uction of the low-temperature photoluminescence (PL) linewidth from 5 meV t o 0.1 meV and a reduced X-ray diffraction CI(RD) rocking curve width from 4 00 to 20 arcsec. As a consequence of the narrow PL linewidths, new features as, e. g. a fivefold fine structure of the donor-bound exciton line at 3.4 71 eV was detected. Additionally, all three free excitons as well as their excited states are visible in PL at 2K. Dry etching techniques for surface preparation allow morphologies of the la yers suitable for device applications. We report on InGaN/GaN multi-quantum -well (MQW) structures as well as GaN pn- and InGaN/GaN double heterostruct ure light emitting diodes (LEDs) on GaN bulk single crystal substrates. Tho se LEDs are twice as bright as their counterparts grown on sapphire. In add ition they reveal an improved high power characteristics, which is attribut ed to an enhanced crystal quality and an increased p-doping.