Ⅲ-族氮化物表層缺陷研究

Abstract

在本論文中，我們研究表面缺陷特性以氮化鎵材料為主並藉由蕭特基元件在不同表面處理的條件下探討電流轉換機制及缺陷密度，並利用特徵電阻(Specific contact resistance)、理想因子(Ideality factor)及特性參數(characteristic energy)作分析。另外為了研究表面缺陷對元件的光電性影響，光檢測器的製作與元件特性經由不同表面處理及熱穏定性也將在論文中一一探討。其中元件在沒有經由電漿式耦合蝕刻(ICP)的條件下，電流轉換機制由熱激發式(Thermionic emission；TE)來主導，另一方面，當元件經由電漿式耦合蝕刻(ICP)的處理後，其電流轉換機制將由熱激發式轉而變成場發式(Field emission；FE)來主導，其原因主要是由於元件使用電漿式耦合蝕刻(ICP)後會在元件表面產生表面缺陷而改變其電流轉換機制，而這些由電漿式耦合蝕刻(ICP)產生的表面缺陷可以經由在高溫600℃氮氣或500℃氫氣下減少並使電流的轉換機制由場發式轉而變成熱激發式，以改善元件的特性。 另外我們使用了電容對頻率(Capacitance-frequency;C-f)的方法去分析元件經由電漿式耦合蝕刻(ICP)後所產生的表面缺陷形式，約可分為s-type、m-type及f-type。其中s-type的表面缺陷主要是來自於元件經由電漿式耦合蝕刻(ICP)處理後所產生的缺陷並可藉由在高溫600℃氮氣或500℃氫氣下減少，另外m-type及f-type的表面缺陷是來自於元件本身的磊晶成長缺陷並亦可利用在高溫氮氣或氫氣下降低缺陷密度。 另一方面光檢測器利用電漿式耦合蝕刻(ICP)後所產生的表面缺陷及高溫處理後，將可產生較高的光響應及內部增益，其中光檢測器光響應藉由在氮氣高溫合金400℃、500℃及600℃下各別為3.95A/W、 0.72A/W及1.85A/W與內部增益在氮氣高溫合金400℃、500℃及600℃下各別為195、36及84。較高的光響應及內部增益主要是由於光檢測器利用電漿式耦合蝕刻(ICP)後所產生的表面缺陷及高溫處理後在其元件的材料特性中，有較多的電洞或電子被補捉，當元件操作在高電場及照光下將藉由這些電洞或電子被補捉與增加碰撞機率產生更多的光電子。

The interfacial defects properties of GaN-based Schottky diodes have been investigated and fabricated by utilized current voltage temperature (I-V-T) and capacitance-frequency (C-f) methods. Surface states effects of metal-semiconductor-metal (MSM) photodetectors (PDs) and p-i-n PDs is applied high reverse electrical field in illumination to confirm the relationship between ICP-induced defects and optoelectric devices characteristics in this dissertation. The current transport mechanisms are analyzed in terms of specific contact resistance ( ), characteristic energy (E00) and ideality factor (η) under different annealing temperatures. The current transport mechanisms of non-treated n-type GaN was TE and was FE based on the finding that the sample by using ICP etching processes. However, the current transport mechanisms can be changed from FE to TE by annealing at 600℃ in N2 ambient or 500℃ in H2 ambient, that is, the current transport mechanism dominates TE or between TE and FE. These results showed that the ICP damages were reduced to a low level and the Schottky diodes characteristics recovered by annealing 600℃ in N2 ambient or 500℃ in H2 ambient. In this dissertation, we have found that the current transport mechanisms are directly dependent on the surface treated conditions, and annealing processes are an effective step in eliminating these defects, and characterize ICP-induced defects such as s-type, m-type and f-type interfacial defects by capacitance-frequency (C-f) methods. The s-type interfacial defects can be reduced by annealing temperature increasing to 600℃ in N2 ambient or 500℃ in H2 ambient. The m-type interfacial defects can be recovered to non-treated n-type GaN by annealing at high temperature in N2 ambient or in H2 ambient. In f-type interfacial defects, annealing in N2 ambient is more effective than that in H2 ambient. The interfacial defects of the Schottky diode with ICP induced defect is dominant s-type, and non-treated sample is dominant f-type. The interfacial defects is f-type indicating the ICP induced defects nearly recovered to non-treated sample, this is the defects result from epitaxial growth such as dislocation or the others. On the other hand, the higher responsivity and internal gain for metal semiconductor metal photodetectors (MSM-PDs) with different surface treatment have been fabricated. The responsivity of MSM-PDs with annealing at 400℃, 500℃ and 600℃ in N2 ambient by applying reverse bias -1Volt is 3.95A/W, 0.72A/W and 1.85A/W, respectively. The internal gain of MSM-PDs with annealing at 400℃, 500℃ and 600℃ in N2 ambient at a photon energy of 3.35eV by applying reverse bias -1Volt is 195, 36 and 84, respectively. The higher responsivity and internal gain characteristics for MSM-PDs with ICP etching process and annealing in N2 ambient at different temperatures are clearly observed. This result may attribute to interfacial states such as holes traps what capture or emit electrons or hole as applied high reverse electrical field and illumination. The persistent photoconductivity effects (PPC) in MSM-PDs with interfacial states by annealing treatment have been studied to confirm the ICP-induced defects exist. Photocurrent gradually increased and the dark current decreased with measured time is observed. These results may also attribute to the presence of holes trap or acceptor-type trap states.