ELECTRICAL AND ESR STUDIES OF GaN LAYERS GROWN BY METAL ORGANIC CHEMICAL VAPOUR DEPOSITION

Abstract

Electrical transport and ESR studies were performed on the state-of-the--art GaN 1ayers grown on sapphire substrate using metal organic chemical vapour deposition technique. For undoped samples electron concentration below 2 x 10 17 cm-1 and mobility up to 500 cm 2 /(V s) were achieved whereas hole concentration up to 7 x 10 17 cm-3 and mobility about 16 cm2 /(V s) were obtained for intentionally Mg doped samples and subsequently annealed. Temperature dependence of mobility was discussed. ESR revealed tle presence of two resonance absorption lines. One of them with g1 = 1.9487 and g|| = 1.9515, commonly observed in n-type GaN was due to shallow donor. The second ESR line was an isotropic one of g = 2.0032 and it is discussed. PACS numbers: 72.80. Ey, 73.61.Ey Gallium nitride has attracted a lot of interest in the last few years as a material of great perspectives for applications in modern optoelectronic devices working in the visible and ultraviolet light range. At the same time extensive studies of GaN crystals have been undertaken but the basic knowledge about this material is still far from satisfactory. One of the major reason limiting both applications as well as better understanding is a problem in obtaining good quality crystals which technology is far more difficult from the standard one used for growth of other III-V compounds. GaN heteroepitaxial layers studied in this paper were grown by horizontal metal organic chemical vapour deposition (MOCVD) using adopted Epigress system in the Crystal Growth Laboratory, Warsaw University. The layers were either undoped or Mg-doped with three different concentrations each of them twice higher than the previous one and subsequently annealed at 750°C using rapid thermal annealing (RTA) method to activate p-type dopant. Sapphire substrates were applied and the growth was initiated with deposition of low temperatures GaN buffer layer. TMG and NH3 served as sources of Ga and Ν respectively, and magnesiu