利用 d-spacing晶格分析技術探討在氮化銦鎵 /氮化鎵 雙量子井結構與由週期性氮化鎵奈米孔隙層形成的分散式布拉格反射器內的應變分佈

Abstract

基於氮化鎵（GaN）結構中的應變分佈會影響其上成長元件的光電特性。本研究利用d-spacing晶格分析技術，探討兩組氮化鎵樣品中晶格常數或應變的深度分佈情形。第一組樣品包含六組氮化銦鎵/氮化鎵（InGaN/GaN）雙量子井結構，其中每個樣品皆依序生長發藍光與綠光量子井，並調變其間距。此樣品組中我們特別關注每個樣品內綠光量子井附近的應變狀態。研究發現，當藍光與綠光量子井的間距越大時，綠光量子井處的壓縮應變越趨緩解。第二組樣品則包含六個分散式布拉格反射器（distributed Bragg reflector 簡稱DBR），其結構由具有不同週期數的週期性多孔層所組成。在每個DBR磊晶結構中，我們採用兩種不同的電化學蝕刻電壓來產生不同的孔隙率，進而達到不同的應變緩解效果。結果顯示，週期數越多，應變緩解越明顯。此外，相較於平行於孔洞延伸方向的平面，在垂直於孔洞延伸方向的平面上，其應變緩解情形更強。同時，較高的施加電壓或較高的孔隙率亦會導致更強的應變緩解。

The strain distribution in a GaN-based structure can affect the optoelectronic behaviors of the devices grown on it. In this research, the d-spacing crystal lattice analysis technique is used to study the depth distribution of lattice constant or strain in two series of GaN-based samples. The first series consist of six InGaN/GaN double-quantum-well (QW) samples, in each of which a blue-emitting and a green-emitting QWs are grown successively with varied separations. We are particularly interested in the strain condition of the green-emitting QW in each sample. It is found that the compressive strain at the depth of the green-emitting QW is more relaxed in a sample of a larger QW separation. The second series include six distributed Bragg reflector (DBR) samples composed of the periodical porous layer of three different period numbers. In each DBR epitaxial structure, two electrochemical etching voltages are used to produce different porosities and hence different strain relaxation conditions. The results show that a larger period number leads to a stronger strain relaxation. Also, in the plane perpendicular to the extension direction of the pipeline-line pores, the strain relaxation is stronger, when compared with that in the plane parallel with the pore extension direction. Meanwhile, a higher applied voltage or a higher porosity results in a stronger strain relaxation.