III- 族氮化物金氧半電晶體於不同基板之特性

Abstract

本論文主要探討兩大部分，第一部分為GaN/AlGaN MOS-HEMT，第二部分為矽基板閘極掘入式GaN/AlGaN MOS-HEMT，首先將實驗中所需之光致電化學(PEC)氧化以及歐姆接觸等參數進行確認，接著是對光致電化學對元件特性的影響進行觀察。 GaN/AlGaN MOS-HEMT的部分，首先在對不同氧化層的生長方式觀察到以PEC方式生長氧化層的元件相較於電漿輔助型原子層沉積(PE-ALD)方式，開關比的部分由7個數量級提升到8個數量級以上，閘極漏電流有2個數量級的優勢。接著在不同PEC氧化層厚度觀察到，隨著PEC的氧化層厚度增加，閾值電壓先向負方向移動後再向正方向移動到-2V，推測閾值電壓可能與PEC氧化層/AlGaN介面狀態有關或與AlGaN與氧化層之間的應力有關。 矽基板閘極掘入式AlGaN/GaN MOS-HEMT的部分，吾人利用光致電化學(PEC)方式生長氧化層，搭配本實驗室的電漿輔助型原子層沉積製作出良好的鈍化層，利用上述參數與閘極掘入(Gate recessed)手段，可製作出增強型元件。閾值電壓的部分從-4V提升到1.5V，然而轉導的部分卻下降約40%，推測利用閘極掘入使通道下方2DEG呈現空乏，使得元件整體串聯電阻上升，造成轉導特性下降。

This work is focused on the use of the photoelectrochemical oxidation (PEC oxidation) method on both AlGaN/GaN on sapphire substrate and gate recessed AlGaN/GaN on silicon substrate to realize metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs). First, the characteristics of PEC oxide layer and plasma enhanced atomic layer deposition oxide layer are compared. The measured results show that, with PEC oxidation, the current on/off ratio is increased from 7 to 8 order of magnitude and the gate leakage current is decreased almost 2 order of magnitude. Then, the effect of different PEC oxide thicknesses to MOS-HEMT performance are considered. We found that with the increasing of the thickness of PEC oxide, the threshold voltage is decreased first then shifted to -2V, which is related to the interface state of the PEC oxide and the AlGaN layer or the strain of the AlGaN layer induced by the PEC oxide. The measured results of gate recessed AlGaN/GaN MOS-HEMTs with PEC oxide layer and PE-ALD passivation layer show that the gate recess method can effectively shift the threshold voltage from -4 V to 1.5 V. However, the transconductance is decreased about 40%.