Luminescence and electron transport properties of GaN and AlN layers

The transport properties of free charge carriers, photo- and cathodo-lumine scence (CV) in GaN and A1N films obtained by MOCVD technique on sapphire an d Si substrates, are investigated. The concentration of free charge carrier s in GaN is of order 10(17)-10(19) cm(-3) whereas A1N thin films are insula ting. The Hall mobility of electrons are 80-140 cm(2)/V s). In undoped GaN films the spectral composition of CL is close to photoluminescence (PL) whe n excited in the region of band-band transitions. The decay time constant o f the 3.44 eV UV emission attributed to the bound exciton is considerably l ess than 1 ns, whereas the 3.26 eV violet (VI) band shows a slow hyperbolic al decay over about 1 mus. The known yellow band appears at 2.25 eV due to transitions via localised states. In A1N the spectral composition of the br oad CL band is close to that from bulk materials attributed to charge trans fer transitions in deep oxygen-related donor-acceptor centres. (C) 2001 Els evier Science Ltd. All rights reserved.