矽奈米點光電特性之研究

本論文研究矽奈米點結構發光二極體的光電特性。施做或不施做砷摻雜的矽奈米點，其光激發光(Photoluminescence,PL)強度相對於溫度的趨勢，兩者呈現相反。無砷摻雜的樣本，溫度由10K升至40K時，電子電洞液體逐漸變成自由激子，造成PL積分強度增加。有砷摻雜的樣本，砷摻雜對矽奈米點造成表面缺陷或損傷，這些缺陷在極低溫的情況下抓住了被釋放的載子，所以溫度由10K升至40K時PL強度逐漸降低；而溫度由40K升至300K時，電子由砷摻雜的矽奈米點被釋放出來而跑到p型矽裏。電子對p型矽是少數載子，所以p型矽基材的發光型復合逐漸增強，PL強度因此逐漸增加。在矽奈米點與p型矽基材之間，有二氧化矽墊層存在時，從矽奈米點發射的載子需要更大的熱活化能才能躍遷過二氧化矽能障進入p型矽。所以PL最低溫度轉移點由40K位移到60K。在無砷摻雜且n型矽基材樣本中，PL強度在溫度40K以上隨著溫度升高逐漸增強。這表示有一種屬於n型矽的少數載子，被從矽奈米點釋放到n型矽基材裏，造成發光型復合機制逐漸增強。因此推論電洞陷阱與電洞釋放是矽奈米點的主要的機制。n型氧化鋅的功能是電子提供層，透明導電膜及抗反射層的角色。包覆在二氧化矽層中的矽奈米點，對載子造成空間的侷限，包覆的二氧化矽層也提供了表面鈍化的效果。經過測量，在室溫下其電激發光(Electroluminescence,EL)外部量子效率可達到0.00043，而且發光的波長正確地對應到矽的非直接能隙能量。有BOE (Buffered Oxide Etch)處理過的矽奈米點樣本，因為表面的受損導致PL強度急遽降低。此樣本再經過氧化鋁表面鈍化層覆蓋後，PL強度馬上顯著地改善。顯示出非常良好的表面鈍化效果從而抑制了在矽奈米點表面載子的非輻射性復合。

關鍵字

矽奈米晶體；光激發光；電激發光；摻雜；非直接能隙能量；發光型復合機制；原子層沉積法；表面鈍化層；氧化鋁；發光元件；外部量子效率；氧化鋅

並列摘要

Optoelectronic characteristics of efficient light-emitting diodes on Si nanodots were investigated. Photoluminescence (PL) of Si nanodots with/without As-doping is opposite. The electron-hole-liquid gradually changes to free exciton from 10K to 40K and caused PL intensity of undoped Si dots increase. PL intensity of As-doped Si dots decreases from 10K to 40K due to defects or damage on the surface of Si dots which created during As-doping process. PL intensity of As-doped Si nanodots increases from 40K to 300K due to increasing electrons released from Si dots to p-Si substrate. These electrons contribute to radiative recombination in p-Si. The lowest temperature point of PL intensity for As-doped Si dots with/without silicon dioxide pad layer is 60K/40K, respectively. Carriers need higher thermal activation energy to overcome oxide energy barrier and move from Si dots to p-Si. Hole trapping and emission is deduced as the dominated mechanism of undoped Si dots. More holes emit from undoped Si dots to n-Si due to temperature increase from 40K to 300K. These minority carriers of n-Si contribute to radiative recombination hence PL intensity increases for undoped Si dot/n-Si substrate. n-ZnO:Al layer grown by atomic layer deposition (ALD) acts as the electron injection layer, transparent conductive window and anti-reflection layer. The silicon dioxide layer surrounding Si dots contributes to spatial confinement of carriers and surface passivation. External quantum efficiency of electroluminescence (EL) up to 0.00043 at the wavelength corresponding to the indirect bandgap of Si was achieved at room temperature. Buffered Oxide Etch (BOE) results in damage of surface of Si nanodots and caused dramatic reduction of PL intensity. Significant enhancement of PL intensity over a wide temperature range was observed from Si nanodots after ALD-aluminum oxide layer deposition, indicating the remarkable surface passivation effect to suppress the non-radiative recombination. Characteristics of light emission from Si nanocrystals will facilitate the development of silicon-based nanoscaled light-emitting devices.

並列關鍵字

Si nanocrystal ； photoluminescence ； electroluminescence ； doping ； indirect bandgap ； radiative recombination ； atomic layer deposition ； surface passivation layer ； aluminum oxide ； light emitting device ； external quantum efficiency ； zinc oxide

參考文獻

[137] M. J. Chen, Light emission from metal-insulator-semiconductor tunneling diodes on silicon, Ph.D. thesis, (Taiwan: National Taiwan University), pp.48-67, 2001

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矽奈米點光電特性之研究

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