Fabrication and Characterization of GaN HEMTs with short gate length

为提高器件性能，研究了GaN hemt的制备工艺，并对制备的器件进行了详细表征。主要结果如下：(1)用Si_3N_4薄膜表面钝化GaN HEMTs可以有效抑制电流崩溃，从而限制输出功率。（ii）利用微拉曼散射光谱成功测量了蓝宝石衬底上GaN hemt的温度分布。温度分辨率优于10K。漏侧边缘处温度最高，形成了高场区。（iii）采用Si_3N_4作为栅极绝缘体的MISHEMT结构抑制了GaN hemt中较大的栅极漏电流。（iv）微肖特基触点的I-V特性测量表明，螺纹位错对栅漏电流没有影响。(v)在0.2 μm长t型栅极的GaN HEMT中获得了54GHz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.