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AlN/GaN metal insulator semiconductor field effect transistor structures (MISFETs) with and without in situ SiNx were investigated. The in situ SiNx passivation layer was deposited using silane and ammonia immediately after the AlN/GaN heterostructure growth by metal organic vapor phase epitaxy. Superior Ohmic quality and improvement of the dc and rf characteristics were obtained with devices made on passivated layers in comparison with unpassivated devices. This enhancement of electrical characteristics is attributed to the fact that the in situ SiNx suppresses the depletion of the two-dimensional electron gas (2DEG) and air exposure while processing. The studies of the in situ SiNx quality and its implication to the 2DEG conducted with Hall, transmission line measurements, capacitance-voltage (C-V) measurements, and photoluminescence measurements showed that the electrical and optical characteristics of AlN MISFET structures were substantially degraded or changed after SF6 plasma treatment.

Structural and optical properties of Fabry-Pérot filters (FPFs) with GaN/air gap based distributed Bragg reflectors (DBRs) were studied. Reflectance of GaN/air gap DBRs on sapphire substrate was calculated from the standard transmission matrix method and results showed that 98% reflectance is achievable with only 3.5 pairs at a center wavelength of 450 nm. The thickness of the GaN layer and the first AlN layer was determined according to the deformation induced by the residual stress. In-plane strain corresponding to growth conditions and the thickness of the GaN epilayer was considered for this analysis. Optical tuning efficiency and spectral range were found to be 0.27 and 25 nm respectively for FPFs with GaN/air gap (322 nm/113 nm) based DBRs and a λ 0 /2 air resonant cavity. The calculated pull-in voltage was 1.5 V. Crack free AlN grown on GaN by in-house MOCVD showed an etching rate of 0.2 nm/min.