氮化鎵之光激光及拉曼特性量測

Abstract

我們針對不同緩衝層厚度及不同摻矽濃度的氮化鎵薄膜進行光激光及 拉曼量測。比較不同緩衝層厚度的光激光結果，我們發現在緩衝層厚度 為100A時有最好的光學性質。而於變溫光激光量測中，我們得到能隙對溫 度的變化量為-4*10^-4 eV/K，施子束縛激子(donorbound exciton)和受 子束縛激子 (acceptor bound exciton)躍遷的活化能 (activationenergy)分別為15和18meV。對於不同摻矽濃度的氮化鎵薄膜 的室溫光激光量測中，我們得到能隙值在純的氮化鎵薄膜中為3.426 eV， 而能隙值隨濃度的三分之一次方(n^1/3)縮減，其斜率為2.34*10-4 eV*cm 。根據拉曼實驗結果，我們發現A1縱向光學聲子(LO)模隨著載子濃度增加 而有藍位移，這主要是因為與電漿子的交互作用(LO phonon-plasmon interaction)。根據此交互作用理論，我們可得到載子濃度大小，其結果 與霍爾量測相符。因此，拉曼量測可謂為量測載子濃度的良好工具。 The photoluminescence (PL) and Raman scattering of GaN films with variousbuffer thicknesses and Si-doping concentrations had been carried out. Good op-tical quality was obtained with 100 A buffer thickness.PL results at differenttemperatures showed a linear temperature coefficient of the gap energy (-4×10^-1 eVK^-1), and the activation energies of donor bound exciton and acceptor bound exciton transitions to be 15 and 18 meV, respectively. For Si-doped GaNfilms, the 300K PL measurements showed the reduced gap depends on carrier con- centration as n^1/3. The concentration coefficient obtained was 2.34×10^-4eV*cm, and the band gap energy in pure GaN film was 3.426 eV.From Raman measure-ments, the A1(LO) mode was observed to shift towards the high frequency and broaden with the carrier concentrations that is due to the LO phonon-plasmon interaction. The carrier concentrations determined by analyzing the LO phonon-plasmon coupled mode agree well with that from Hall measurements. Therefore, the Raman scattering is a suitable technique to study the phonon-plasmon interaction in GaN.