Properties of group III nitrides grown in production type MOVPE systems

摘要

Due to an increased interest in the large scale production of GaN-based devices we have used our AIXTRON single wafer horizontal tube and Multiwafer Planetary(R) MOVPE systems for the fabrication of GaN/InGaN/GaN heterostructures, multiquantum well structures and LEDs. The AM 2000HT was set up in a configuration of 7/spl times/2 inch which provides unique uniformity capabilities due to the two fold rotation of the substrates. Thickness homogeneities and In composition have been shown to be around 1% on full 2 inch wafers. Wafer to wafer homogeneity of InGaN emitting at 440 nm at 300 K is also around 1%. Reproducibly we obtained resistivities of the GaN:Mg top layer of less than 1 /spl Omega/cm which corresponds to 5-10/spl times/10/sup 17/ cm/sup -3/. Simple GaN/InGaN LED test structures were fabricated to investigate the doping and the In incorporation mechanisms. Several DH, SQW and MQW LED test structures were grown and processed. Current-voltage characteristics, output power and the wavelength distribution were measured to evaluate the epitaxial growth. We fabricated LED test structures with peak wavelengths between 400-530 nm depending on layer structure and chosen In composition in the active layer. Electroluminescence (EL) of the QW and DH LED test structures resulted in intense violet and blue emission which was clearly visible under normal room light. LED test structures with 4 nm InGaN active region show a peak wavelength up to 460 nm with a FWHM of /spl sim/35 nm. Stimulated emission and optically pumped laser action was used to investigate the material quality for future laser applications. Room temperature gain spectra of MQW structures show a threshold value for the optical amplification of 200 KW/cm/sup 2/ and gain values up to 140 cm/sup -1/. The reported investigation of the optical properties and of the laser parameters under optical excitation clearly indicates the increased sample quality depending on growth parameters such as growth temperature, switching sequence, control of parasitic adduct formation or total pressure in the reactor.