AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM+NS-MoM

Paper EM+NS-MoM7
High Reflectance GaN-based Distributed Bragg Reflectors Grown on Si Substrates

Monday, October 31, 2005, 10:20 am, Room 310

Session: Novel Approaches in Wide Bandgap Semiconductors
Presenter: M.A. Mastro, U.S. Naval Research Laboratory
Authors: M.A. Mastro, U.S. Naval Research Laboratory
R.T. Holm, U.S. Naval Research Laboratory
N.D. Bassim, U.S. Naval Research Laboratory
D.K. Gaskill, U.S. Naval Research Laboratory
C.R. Eddy Jr., U.S. Naval Research Laboratory
R.L. Henry, U.S. Naval Research Laboratory
M.E. Twigg, U.S. Naval Research Laboratory
Correspondent: Click to Email
Presently, GaN based optoelectronic devices are primarily grown on expensive sapphire and SiC substrates. Substituting these substrates with inexpensive Si substrates would represent a major shift in the economics of the visible optoelectronic market. The primary limitation to this device structure is light absorption by the opaque Si substrate. Insertion of a high reflectance distributed Bragg reflector (DBR) between the substrate and the active region would increase light extraction by approximately a factor of two. The second major impediment to this device structure is the poor quality of group III-nitride films grown on Si substrates. High densities of dislocations and cracks can form in the (Al,Ga,In)N layers due to their large lattice and thermal expansion mismatch with the Si substrate. Thus low internal quantum efficiency is commonly observed for GaN based devices grown on Si substrates. This paper presents the first high-reflectance (>90%) (Al,Ga)N quarter-wave DBR grown on a Si (111) substrate. In-situ reflectometry of the MOCVD growth process allowed exact control of each individual layer thickness to yield DBR reflectance approaching the calculated theoretical level. Nominally crack free structures were obtained by controlling the distribution of the strain in the structure. Specifically, the DBR structure acted as a distributed buffer layer (DBL) for the thick GaN cap layer. TEM revealed a fall-off in screw-type dislocations throughout the DBL. This development presents the opportunity to significantly advance GaN based optoelectronics, including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs) and vertical cavity surface emitting lasers (VCSELs), on Si substrates.