在InAlP/InGaAs 假晶式高電子遷移率電晶體結構之蕭基金屬接觸之研究

Abstract

本論文之實驗研究目的是在製作具有寬能隙及高能隙差之磷化銦鋁假晶式高電子遷移率電晶體，以期能達到高崩潰電壓,高蕭基位障高度之特性，用於製作高功率放大器以應用於微波無線通訊. 我們將研究鈦/鉑/金、鉑/鈦/鉑/金及鎢/鈦/鉑/金 蕭基接觸金屬在磷化銦鋁材料上的特性,並以電流、電容量測、穿透式電子顯微鏡及X光繞射分析接觸金屬經過不同溫度退火擴散對於元件特性之影響. 蕭基二極體特性下降均會造成閘極漏電流,片電阻,理想係數的上升及位障高度之下降.由材料分析及電性量測顯示以鎢作為蕭基金屬的二極體於500度退火30分鐘後其蕭基特性仍保持穩定,此物性也同時反應在理想係數及能隙高度經過退火後的熱穩定性.由此可知以鎢/鈦/鉑/金為蕭基金屬元件在長時間及高溫下使用是個良好的選擇. 在PHEMT元件製作方面,本實驗中嘗試鍺/金/鎳/鈦/金歐姆接觸退火處理後可達到電阻係數為5×10-7 Ω-cm2並以光學微影方式完成0.4μm閘極.在0.4μm閘極長度及40μm閘極寬度之元件上所得到的磷化銦鋁/砷化銦鎵假晶式高電子遷移率電晶體具有241mA/mm的最大電流密度,67mA/mm 飽和電流及11V的閘極-汲極崩潰電壓和最大互導係數為302mS/mm. 0.5μm×125μm E-mode 磷化銦鋁/砷化銦鎵假晶式高電子遷移率電晶體也同時被製作並擁有最大電流密度183mA/mm於閘極電壓2.5V,最大互導係數為206mS/mm,14V的閘極-汲極崩潰電壓及門檻電壓209mV.其可擁有於高達2.5V閘極電壓下仍無崩潰應是由於磷化銦鋁層造成的高起始電壓所致. 本論文同時以Ti/Pt/Au, Pt/Ti/Pt/Au 和 W/Ti/Pt/Au 為蕭基金屬製作InAlP/InGaAs PHEMT藉此瞭解上述蕭基金屬擴散對於元件特性的影響.

In this dissertation, In0.5Al0.5P/InGaAs PHEMTs are expected to have a high breakdown voltage, high schottky barrier height for microwave power device applications due to the improvement of a larger delta EC (0.45eV) and a wide bandgap of InAlP schottky barrier layer. We studied the schottky contact of Ti/Pt/Au, Pt/Ti/Pt/Au, W/Ti/Pt/Au on InAlP schottky layer. I-V measurement, C-V measurement, XRD, TEM analysis were performed to examine the diffusion of metal and InAlP layer in details. The schottky diode degradation exhibits an increase in reverse gate leakage current, sheet resistance, ideality factor, and a decrease in schottky barrier height. Electrical studies of W/Ti/Pt/Au schottky contact have shown that aging at 500°c for 30 minutes does not significantly change the schottky diode characteristics and this is reflected in the high thermal stability of schottky barrier height and ideality factor. From this study, W/Ti/Pt/Au is proved to be a good schottky metal for long time and high temperature operations. A Ge/Au/Ni/Ti/Au(700/1400/500/200/1000A) ohmic contact scheme has been investigated to form low resistance with a minimum contact resistivity of about 5×10-7Ω-cm2. The 0.4μm optical gate was fabricated and applied to the InAlP PHEMTs. A DC characteristic of Imax of 241mA/mm, Ids of 67mA/mm and a maximum transconductance of 302mS/mm at VDS=1.5V were measured with a 0.4μm long and 40μm wide device. The 0.5μm×125μm Enhancement-mode InAlP/InGaAs device exhibited a maximum drain current of 183 mA/mm at gate biasd on +2.5 V with a gate-to-drain breakdown voltage of -14V. The maximum transconductance of the device was 206 mS/mm and the threshold voltage was 209 mV. The fabricated 0.5μm×125μm Enhancement-mode InAlP/InGaAs device can be operated with gate voltage up to 2.5V owing to its high schottky turn on voltage. In order to realize the influences of schottky metal diffusion after annealing, the dependence of gate metal on the performance of InAlP/InGaAs PHEMTs are also examined for Ti/Pt/Au, Pt/Ti/Pt/Au, and W/Ti/Pt/Au metals.