Growth and device applications of III-nitrides by MBE

This paper reviews progress in the heteroepitaxial growth of III-nitrides b y plasma-assisted MBE. The role of nucleation layers in determining the pol arity of these films is addressed. Doping of GaN with silicon leads to n-ty pe films whose carrier concentration can be controlled between 10(16) and 1 0(20) cm(-3). P-type doping with Mg with free carrier concentration of up t o 5 x 10(18) cm(-3) has been attained without requiring post-growth anneali ng. The epitaxial growth of AlGaN and InGaN alloys is addressed. AlGaN allo ys were shown to undergo either one monolayer or seven and 12 monolayer sup erlattice ordering along the [0 0 0 1 6] direction, which is also the direc tion of growth. The InGaN alloys were found to undergo both ordering as wel l as phase separation. InGaN/GaN and GaN/AlGaN MQWs have been fabricated an d found to show good radiative recombination efficiency. Carrier transport in lightly doped GaN films is anisotropic in tile directions parallel and p erpendicular to the substrate. In the parallel direction the mobility is re duced by dislocations while in the vertical direction the mobility attains values about 1000cm(2)/Vs, close to the theoretical prediction. AlN/GaN dis tributed Bragg reflectors (DBRs) with reflectivity 99% have been fabricated . (C) 2001 Elsevier Science B.V. All rights reserved.