Influence of Metalorganic Vapor Phase Epitaxy Regrowth on Characteristics of InAlN/AlGaN/GaN High Electron Mobility Transistors

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We fabricated InAlN/AlGaN/GaN heterostructures using a regrowth technique in order to avoid an unintentional Ga incorporation into the InAlN barrier layer. We prepared two types of samples (S1 and S2) using different regrowth sequences: InAlN regrowth on AlGaN/GaN (S1), and InAlN/AlGaN/GaN regrowth on GaN (S2). The characteristics of the high electron mobility transistors (HEMTs) differed depending on the adopted sequence. In current--voltage characteristics, the kinks appear only for the HEMTs using S1 (HEMT-S1). The current reduction induced by gate-bias stress is as large as 20% in HEMT-S1, while it is only 5% in HEMT-S2. Results of our complementary experiments on AlGaN/GaN heterostructures prepared by various regrowth sequences suggest that the inferior device properties of HEMT-S1 can be attributed to higher trap density at the regrowth interfaces. The higher trap density is most likely a result of the AlGaN surface's being more easily oxidized than the GaN surface. Non-uniform decomposition of the AlGaN surface during the heating process prior to the regrowth may also play a role. The fairly a good device performance of HEMT-S2 indicates that InAlN can actually act as a good barrier for GaN-based HEMTs by careful optimization of the fabrication sequence even with a regrowth process.
2013-04-25