Final report on LDRD project : outstanding challenges for AlGaInN MOCVD.

Abstract

The AlGaInN material system is used for virtually all advanced solid state lighting and short wavelength optoelectronic devices.Although metal-organic chemical vapor deposition (MOCVD) has proven to be the workhorse deposition technique, several outstanding scientific and technical challenges remain, which hinder progress and keep RD&A costs high. The three most significant MOCVD challenges are:(1) Accurate temperature measurement.(2) Reliable and reproducible p-doping (Mg).(3) Low dislocation density GaN material. To address challenge (1) we designed and tested (on reactor mockup) a multiwafer, dual wavelength, emissivity-correcting pyrometer (ECP) for AlGaInN MOCVD. This system simultaneously measures the reflectance (at 405 and 550 nm) and emissivity-corrected temperature for each individual wafer, with the platen signal entirely rejected. To address challenge (2) we measured the MgCp 2 + NH 3 adduct condensation phase diagram from 65-115°C, at typical MOCVD concentrations. Results indicate that it requires temperatures of 80-100°C in order to prevent MgCp 2 + NH 3 adduct condensation. Modification and testing of our research reactor will not be complete until FY2005. A new commercial Veeco reactor was installed in early FY2004, and after qualification growth experiments were conducted to improve the GaN quality using a delayed recovery technique, which addresses challenge (3). Using a delayed recovery technique, the dislocation densities determined from x-ray diffraction were reduced from 2x10 9 cm -2 to 4x10 8 cm -2 . We have also developed a model to simulate reflectance waveforms for GaN growth on sapphire.