以矽基板開發常關型氮化鎵高電子移動率電晶體

Abstract

我們利用Aixtron 2000HT GaN MOCVD，開發氮化鎵 (GaN) 在矽基板上的磊晶技術，並提出NiOx絕緣層與奈米柱的結構，開發高電流常關型(normally off) 氮化鎵高電子移動率電晶體(HEMTs)。其摘要如下: 1. 利用linear graded AlGaN緩衝層磊晶設計，克服發氮化鎵與矽基板的晶格係數與導熱係數的差異，開發無crack與pits的GaN/Si template，其XRAY 量測 半高全寬(102)~570 arcsec 。 2. 利用Carbon doped在AlGaN緩衝層的方式，其濃度為1x1017cm-3，可將HEMTs的崩潰電壓從279V提高到860V。 3. 在經過磊晶實驗,為達到高二維電子氣濃度,需拉高AlGaN的鋁含量與兼顧磊晶層品質，應採用Al0.34Ga0.66N磊晶層， 其Resistivity為342□/sq， mobility為1280cm2/v-s， Sheet Concentration為1.4x1013cm-2，做成HEMTs量測，其導通電阻為10.08m□-cm2，導通電流為311mA/mm。 4. 在閘極下方採用nano rod結構，可使存有部分2DEG channel,可使D mode HEMTs轉變為E-mode HEMTs，其臨界電壓從-2V shift到+2V，同時最大導通電流只微降9.5%。 5. 開發NiOx當作閘極下方的絕緣層，可以將漏電流從0.01mA/mm下降至<50nA/mm，並將Ion/Ioff ratio從3.5 x 105提高至2.1 x 108。 6. 利用高濃NiOx，當作閘極下方的絕緣層，有較低的次臨限斜率，GaN HEMTs 有較佳的normally off特性表現。

This paper presents an approach in GaN/Si epitaxy technology by Aixtron 2000HT MOCVD. We also fabricate normally off AlGaN/GaN high electron mobility transistors (HEMTs) with nano rod structure. The major results are as follow: 1. Using the linear graded AlGaN buffer layer to overcome lattice mismatch and thermal expansion differences between GaN and Silicon substrate. The XRD FWHM (102) was 570 arcsec of GaN/Si template without crack and pits. 2. The breakdown voltage has been improved from 279V to 860V by carbon doped at AlGaN buffer layer. The concentration of carbon doped was 1x1017cm-3. 3. The Al0.34Ga0.66N barrier layer of the HEMTs have high two-dimensional electron gas concentration (2DEG). The mobility, 2DEG density, and sheet resistance was 1280 cm2/Vs, 1.4x1013 cm-2 and 342 □/sq., respectively. After HEMTs fabricating, the on-state resistance and drain current was 10.08 m□-cm2 and 311 mA/mm., respectively. 4. The 2DEG channel has been discontinued intermittently with the nano rod structure at the gate region. The HEMTs have been converted to E-mode and the drain current sharp drop could be avoided. The threshold voltage can be shifted from -2V to+ 2V. The maximum transconductance decreased slightly 9.5%. 5. The leakage current from 0.01 mA/mm decreased to 50 nA/mm and Ion/Ioff ratio improved from 3.5 x 105 to 2.1 x 108 by NiOx gate insulating layer deposited. 6. The normally off HEMTs with the lower subthreshold swing could be achieved by high concentration NiOx insulating layer under the gate region.