Fabrication and Characterization of GaN HEMTs with short gate length

为了提高GaN HEMTs的性能，研究了GaN HEMTs的制备工艺，并对所制备的器件进行了详细的表征。主要研究结果如下。(1)Si_3N_4膜表面钝化GaN HEMT能有效地抑制限制输出功率的电流崩塌。(Ii)用显微拉曼散射光谱成功地测量了蓝宝石衬底上GaN HEMT的温度分布。获得了优于10K的温度分辨率。最高温度出现在漏极一侧形成高场区的边缘。(3)用Si_3N_4作栅绝缘体的GaN HEMT中观察到了较大的栅漏电流，而MISHEMT结构抑制了这种漏电流。(4)微肖特基接触的I-V特性测量表明，穿线位错对栅漏电流没有影响。(V)采用0.2μm长T形栅的gan HEMT获得了54 GHz的电流增益截止频率。

Fabrication process of GaN HEMTs was studied to improve the device performance, and the fabricated device was characterized in detail. The main results are as follows. (i) Surfacepassivation of GaN HEMTs with Si_3N_4 film was effective in suppressing the current collapse that limit the output power. (ii) Temperature distribution in GaN HEMTs on a sapphire substrate was successfully measured by micro-Raman scattering spectroscopy. Temperature resolution better than 10K was obtained. The highest temperature was obtained at the edge on the drain side where high-field region was formed. (iii) A large gate leakage current was observed in the GaN HEMTs, which was suppressed by employing MISHEMT structure, where Si_3N_4 was used as a gate insulator. (iv) Measurement of I-V characteristics of micro-Schottky contacts revealed that the threading dislocation did not affect the gate leakage current. (v) Current gain cutoff frequency of 54GHz was obtained in the GaN HEMT with 0.2-μm-long T-shaped gate.