表面下氮化鎵孔隙結構造成的應力釋放對上層量子井發光行為之影響

Abstract

我們利用磊晶技術依序成長重度矽摻雜的氮化鎵層與三週期氮化銦鎵/氮化鎵量子井樣結構，以此製作三種不同形狀與大小的平台結構並在重度矽摻雜的氮化鎵層中利用電化學蝕刻製作孔洞結構，由此使上層量子井所受到的壓縮應力得以釋放。藉由量測量子井發光的光譜、內部量子效率及時域衰減時間，探討不同應力釋放效果對量子井發光行為的影響。應力釋放造成量子井發光行為變化，包含發光波長藍移、內部量子效率增加及時域衰減時間變短。平台內的孔洞結構進一步釋放應力，使發光行為變化越大。雖然我們能觀察到在相對較大尺寸的平台內製作具有方向性的孔洞結構能造成應力釋放的各向異性，但對量子井發光的偏振行為影響不大。

Mesas of three different geometries and porous structures (PSs) in the mesas are fabricated on an epitaxial sample consisting of a three-period InGaN/GaN quantum well (QW) structure above a heavily Si-doped (n++-GaN) GaN layer such that the compressive strain in the QW structure is relaxed. The PSs are formed through an electrochemical etching (ECE) process. Through the measurements of QW emission spectrum, internal quantum efficiency (IQE), and photoluminescence (PL) decay time, we study the effects of various strain relaxation conditions on the QW emission behavior. A stronger strain relaxation condition results in the larger changes of QW emission behavior, including the blue shift of emission spectral peak, the increase of IQE, and the reduction of PL decay time. In a mesa with a PS, the strain relaxation is stronger than that in a solid mesa, leading to a larger change of QW emission behavior. Although the strain relaxation anisotropy can be clearly observed due to the oriented pore extension of a PS in a mesa of a relatively larger size, the polarization dependence of QW emission behavior is weak.