Electrical and Optical Characterization of AlGaN/GaN HEMTs with In Situ and Ex Situ Deposited SiNx Layers

A comparative study of AlGaN/GaN high-electron-mobility transistor (HEMT) surface passivation using ex situ and in situ deposited SiNx is presented. Performing ex situ SiNx passivation increased the reverse gate leakage and off-state channel leakage by about three orders of magnitude. The in situ SiNx layer was characterized using transmission electron microscopy (TEM) and capacitance–voltage (CV) measurements. Photoluminescence (PL) spectra indicated a reduction of nonradiative recombination centers in in situ SiNx-passivated samples, indicating improved crystal quality. CV measurements indicated a reduction of surface state density as well, and thus better overall passivation using in situ SiNx. Electroluminescence (EL) images of the channel regions in AlGaN/GaN HEMT devices operating in forward blocking mode with up to 400 V drain bias demonstrated reduced channel emission profiles of in situ-passivated devices. Compared with a nonpassivated reference sample, the reduced EL emission profiles correlated with a reduced channel temperature on ex situ SiNx-passivated devices.

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