同電子性銦及鎵摻雜氮化鎵薄膜之時間解析光譜研究

Abstract

在本論文中，我們利用時間累積光譜(time-integrated PL)以及時間解析光譜(time-resolved PL)的方法，研究同電子性銦及鎵摻雜的氮化鎵薄膜的光學特性。對於35nm及60nm緩衝層厚度的未摻雜氮化鎵，其施子束縛激子(I2)躍遷之生命週期隨著溫度的1.5次方呈比例。從Shockley-Read-Hall的理論模型中，我們也可以推導出生命週期與trap濃度之間的關係，在60nm緩衝層厚度的氮化鎵樣品之中，其trap的濃度似乎是3倍於35nm緩衝層厚度的氮化鎵。對於銦摻雜的氮化鎵薄膜，我們發現I2的生命期與溫度以及銦流量的大小無關，這種現象可能是由於同電子性銦摻雜的本質效應。對於砷摻雜的氮化鎵薄膜，當溫度從10K增加到75K時，I2的生命期會從105ps呈指數性型態的減少至40ps，然後當溫度繼續升高至250K時，生命其則是增加至72ps，這種行為我們認為是同電子性砷原子在氮化鎵中產生了非常靠近淺階能階的位能井，並且預先主導了整個載子的復合機制。

We have studied the isoelectronic (In and As) doping effects on the optical characteristics of GaN films by time-integrated and time-resolved photoluminescence. For undoped GaN with a buffer layer of 35 nm and 60 nm, the decay time of neutral-donor-bound exciton (I2) transition increases with T1.5. From the Shockley-Read-Hall (SRH) model, we can deduce the relationship between the lifetime and the trap concentration. The GaN of 60 nm buffer thickness appears to have 3 times more trap concentration than that of 35 nm one. For In-doped GaN, we have observed the decay time of the I2 line that is almost independent of the temperature and In source flow rate. These observations might be attributed to the intrinsical characteristics of isoelectronic In doping. For As-doped GaN, the I2 decay time first decreases exponentially from 105 ps to 40 ps between 10 K and 75 K, and then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities itself in GaN, which generate near-by shallow levels that predominate the recombination process.