集極在上氮化鎵/氧化鋅異質接面雙極性電晶體

GaN/ZnO collector-up Heterojunction Bipolar Transistors

李慶泰(Ching-tai Li)

指導教授 ： 辛裕明

國立中央大學/資訊電機學院/電機工程學系/碩士(2007年)

摘要

本論文前部分為概述濺鍍原理及氧化鋅薄膜製作流程，並利用霍爾量測、X光繞射量測分析氧化鋅層在不同的退火溫度下遷移率、濃度及電阻率等特性，提出以平臺式（Mesa-type）及重新成長法（Regrowth Method）的製程方法製作完成氧化鋅/氮化鎵二極體、氮化鎵/氧化鋅異質接面雙載子電晶體（GaN/ZnO Heterojunction Bipolar Transistors），且對電晶體進行直流量測、分析與討論，完成之元件製程均於國立中央大學光電科學研究中心完成。元件量測部份主要包括室溫直流特性、低溫直流特性；量測的射極面積主要為Ac= 150×150 um2，最後對量測結果進行討論和分析。
此電晶體在常溫無真空環境下VBE=2.4V時所得到電流增益約為11，崩潰電壓大於3伏特，且此電晶體在低溫200k、100k下所量測之電流增益分別約為620及1200，最後亦證明無蝕刻p-Type氮化鎵有較佳的金屬和半導體特性。

關鍵字

濺鍍 ； 重新成長法 ； 氮化鎵 ； 異質接面雙極性電晶體 ； 氧化鋅

並列摘要

Several problems related with GaN-based bipolar transistors result in difficulties to fabricate GaN-based HBTs with good device characteristics. The major problems are the Schottky-like Ohmic contacts on p-GaN and the leakage paths from the threading dislocations (TDs) and dry etching process. Therefore, the research on GaN-based HBTs is still one of the challenging research subjects. The leakage current at the base-collector junction is the major source of the non-ideality in device characteristics. In order to reduce the threading dislocations from the GaN/sapphire interface and dry etching damage on p-GaN while fabricating a regular emitter-up HBT, a collector-up structure is used in this study. In this study we present a GaN/ZnO collector-up HBT with ZnO deposited by dc sputtering. The GaN based emitter and base structures are grown by MOCVD. Then n-ZnO film is deposited and lifted-off on top of the p-InGaN by dc sputtering with subsequent annealing at 600 degree for 60 seconds. The dependence of carrier concentration, electrical resistivity and Hall mobility of ZnO films on the annealing temperatures are studied. The as-deposited ZnO film does not show the Hall results due to the high resistivity. But lower resistivity is observed by increasing annealing temperatures. The x-ray scattering intensity profile of a 2θ-ω scan across the (002) reflection of the studied n-ZnO films is examined. It is shown that the diffraction angles of the annealed ZnO films remain the same as the GaN without shifting. After ZnO is lifted-off to define the collector region, base metallization is done by deposition of Ni/Au without dry etching. Finally, both emitter and collector contacts are completed with Cr/Au. The measured Gummel plot shows maximum current gain of ~11 with turn-on voltage of 2.25V (at 1uA). The measured common-emitter I-V characteristics demonstrate a working transistor with similar current gain. The Early voltage is low due to the low p-type doping in the base region. The off-set voltage (~1.2V) observed in the common-emitter I-V is mainly attributed to the different turn-on voltages between the base-emitter and base-collector junction diodes. The turn-on voltages (at 1uA) of the base-emitter and base-collector junction diodes are 2.4 and 1.25 V, respectively. The preliminary results of the fabricated GaN/ZnO HBT demonstrate the possibility of using wide band-gap ZnO on GaN to introduce more interesting research topics. In addition, the collector-up HBT structure could be an effective way to avoid the high threading dislocations in the base-collector junction of emitter-up HBT and thus improve the base-collector leakage problems.

並列關鍵字

GaN ； sputter ； ZnO ； HBTs ； Regrowth

參考文獻

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