Analysis of carrier mobility and concentration in Si-doped GaN grown by reactive molecular beam epitaxy

Abstract

Quantitative information on acceptor concentration, donor concentration and donor activation energy has been obtained for Si-doped GaN epitaxial layers grown by reactive MBE through simultaneous fitting of the temperature dependent Hall mobility ( μ) and carrier concentration ( n) data. The analysis indicates that the electron mobility at high temperatures is significantly influenced by crystal defects. But the dominant scattering at low temperatures is by ionized impurities. Fitting the mobility data over a wide temperature range yields a good estimate of 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 important because the fitted value of E D is very sensitive to the value of N A. For a good fit, two donor levels had to be used in all the Si-doped GaN layers except in a sample grown at relatively lower temperature. The thermal activation energies of the shallower donor levels determined in different samples range from 4.5 to 8.9 meV, and are consistent with screened hydrogenic donors in GaN. The deeper levels are from 77 to 122 meV in different samples and not hydrogenic.