針對表面下氮化鎵孔隙結構造成應力釋放的晶格常數分析研究

Abstract

在這論文研究中，我們使用晶格d-spacing分析技術，探討兩種不同磊晶結構所製作三種不同平台結構樣品的應力釋放行為。這些應力釋放是由平台和表面下多孔結構這兩個因素所引起。在連續或調變的電流下，經由電化學蝕刻過程形成表面下多孔結構。當平台尺寸較小（約100微米）時，台面結構主導應力釋放的結果。當平台尺寸較大（>300微米）時，多孔隙結構在應力釋放中扮演重要的角色。多孔隙結構內的定向孔隙延伸導致非均向應力釋放。在電化學蝕刻過程中使用調變電流，我們可以觀察到週期性的低孔隙率環狀帶，其方向與蝕刻溝槽延伸方向垂直。這些低孔隙率帶在電化學蝕刻電流啟動後形成。在多孔隙結構內出現這些低孔隙率帶後，應力釋放變得較弱。

In this thesis research, we investigate the strain relaxation behaviors of the four samples of two different epitaxial structures and three different mesa structures based on the technique of d-spacing crystal lattice analysis. The strain relaxations are produced by the two factors of mesa fabrication and the formation of subsurface porous structure (PS). A PS is formed through an electrochemical etching (ECE) process with either continuous or modulated current supply. When mesa size is small (~100 micron), the effect of mesa fabrication dominated the strain relaxation result. When mesa size is large (>300 micron), PS plays a more important role in strain relaxation. The oriented pore extension in a PS results in the behavior of anisotropic strain relaxation. With modulated current supply in an ECE process, periodic ring bands of lower porosities can be observed with their orientation perpendicular to the etched trench extension direction. Such low-porosity bands are formed right after ECE current is switched off and turned on. With such low-porosity bands in a PS, the strain relaxation effect becomes weaker.