氮化鎵二極體電性與缺陷分析

Abstract

寬能隙半導體材料氮化鎵最近幾年格外受到重視,因其 可製成藍光二極體與藍光雷射,以及在紫外波長的應用,但其目前對其研究 大多為元件製做特性,對其物理特性探討尚屬有限,本論文為對不同分子源 TEGa和TMGa成長的GaN做電性與缺陷上的研究. 在氮化鎵蕭特基二極體 能障高度之量測上,我們以三種方法進行量測,以I-V,I-T量測方法所得之 能障高度為0.89eV與0.76eV,接近理論所得之0.84eV,但以C-V量測方法所 得之能障高度,由於受到串聯電阻及其他因素的影響,較其他方法為大,約 為1.12eV,但經由對其做阻抗分析後,再回復回來而得到之能障高度為0.82 eV,對此我們可以對其接面的特性再加以深入的研究. 在缺陷分析上, 我們以暫態電容量測氮化鎵的缺陷能階,在TEGa中量到一個缺陷能階0.60 eV,在TMGa中則有兩個缺陷能階1.10eV與1.27eV,其中TMGa所得到的Et1與 Et2與其他研究群以PL光譜所得到的2.2eV的yellow emission 應有相當的 關係,造成氮化鎵這些深層缺陷的原因,由於長晶條件,溫度,所用分子 源....等不同,所以仍不清楚是何種原因所造成,只能推測可能與NGa與氧 污染有關. 在照光與否對暫態電容的量測上,兩種樣品的暫態電容響應 對光激發都非常敏感,可見得在GaN中可能存在非常深的缺陷能階,可利用 光將位於在此缺陷內的載子激發出來,去除光源之後與加光源之前兩者之 電容差值即代表缺陷濃度,對TEGa而言電容差值為1pF,TMGa為3pF,經過計 算之後對應到TEGa與TMGa的缺陷濃度至少為4.8xE(15)cm-3與2.16xE(16) cm-3 由於GaN具有非常深的深層缺陷不易於量測,而我們以此種量測方 法所得之結果雖然無法直接得到極深層的缺陷活化能,但可對其缺陷濃度 做概略的估計,因此由以上的結果,可作為日後改進磊晶品質的參考,減少 缺陷對材料的影響,已獲得更好之電性與發光效率. Wide bandgap GaN has been considered as the promising blue,UV source and high temperature, high power electronic devices. Recent introduction of commerical blue and blue_green LED's based on GaN and its alloys have attracted great activities in the area. In the report, we present our studies of the electric characterizatons onschottky barrier GaN samples grown on sapphire by a low-pressure metal organicchemical vapor deposition (LP-MOCVD) system. Trimethyl- gallium (TMGa) and Triethyl-gallium (TEGa) were separately used for Ga sources for the growth of GaN samples. Barrier heights of 0.89ev and 1.12ev were measured from the current-voltage and capacitance-voltage characteristics, respectively. The much higher barrierheight measured by the capacitance methid is due to a large series resistance. The effects of this series resistance on the doping and spectroscopy. After thecorrection of the resistance, a barrier height of 0.82ev was obtained, consistent with the I-V result. Transient capacitance method was used to characterize the properties of the GaN deep-level states. A deep-level state with an activation energy of 0.60eV were observed for GaN grown with TEGa source and two deep level at 1.10eV and1.27eV were observed in TMGa sample. Very deeper states were probed by measuring the difference of transientcapacitance before and after illumination.The difference of capatiance was equal to 1pF and 3pF were observed for TEGa and TMGa samples, respectively. Thesecapacitance differences correspond to concentrations of at least 4.8xE (15)cm-3 and 2.16xE (16) cm-3 for very deeper states