ANALYSIS OF CARRIER MOBILITY AND CONCENTRATION IN SI-DOPED GAN GROWN BY REACTIVE MOLECULAR-BEAM EPITAXY

Quantitative information on acceptor concentration, donor concentratio n and donor activation energy has been obtained for Si-doped GaN epita xial layers grown by reactive,MBE through simultaneous fitting of the temperature dependent Hall mobility (mu) and carrier concentration (n) data. The analysis indicates that the electron mobility at high tempe ratures is significantly influenced by crystal defects. But the domina nt scattering at low temperatures is by ionized impurities. Fitting th e mobility data over a wide temperature range yields a good estimate o f the acceptor concentration (N-A) in the sample which is then used as a known parameter in the fit to the n vs T data in order to determine the other important parameters, namely the donor activation energy (E -D) and donor concentration (N-D). Correct estimation of N-A is very i mportant because the filled value of E-D is very sensitive to the valu e of N-A. For a good fit, two donor levels had to be used in all the S i-doped GaN layers except in a sample grown at relatively lower temper ature. The thermal activation energies of the shallower donor levels d etermined in different samples range from 4.5 to 8.9 meV, and are cons istent with screened hydrogenic donors in GaN. The deeper levels are f rom 77 to 122 meV in different samples and not hydrogenic. (C) 1998 El sevier Science Ltd. All rights reserved.