氮化鎵面射型發光元件之研究

Abstract

氮化鎵垂直共振腔面射型雷射元件(VCSEL)由於磊晶技術上的困難，以致於難以獲得高品質的共振腔，這個主要的因素使得到目前為止藍光VCSELs的製造尚未能成功。本實驗室在具有成長共振腔特性的發光元件之技術下，進行元件的製程研究，以累積GaN VCSEL的製程經驗。 本論文主要研究氮化鎵面射型發光元件製造的相關技術，在元件設計方面：採用3λ的微共振腔腔長，此設計能兼顧元件特性與製程需求。元件結構上為採用目前最有機會成功製造藍光面射型雷射的內部共振腔(Intra-cavity)形式的結構:下層DBR反射鏡採用氮化鋁與氮化鎵材料來成長，由於這兩材料的折射率差異較大，所以可以較少的磊晶層數，便可以達到高的反射率；上層介電質DBR採用二氧化矽與二氧化鈦材料，這兩種材料由於蒸鍍技術成熟且可用在藍光波段，所以較易達到高反射率的目標。 在元件製程程序方面，由於採用內部共振腔且元件為微共振腔之結構，所以在蝕刻深度的控制及電流侷限的設計上，都較一般發光元件來的困難。另外，在蒸鍍介電質DBR的製程方面，由於一般光阻處於高溫的蒸鍍環境，會產生過度硬化的結果導致剝離(Life-off)的製程失敗，我們提出以LOR溶劑來克服上述的缺點，使剝離製程能成功達成。 本實驗已完成電激發面射型發光元件，其電激發螢光波長位於410.6 nm、半高寬為7.4 nm，共振腔的品質因子約為55.5。由實驗結果可知其發光波長已受到共振腔中光模態的限制。

GaN Vertical cavity surface emitting laser (VCSEL) acknowledged basic difficulty is in in-situ epitaxial growth technology to form high quality resonant cavity. This resulting GaN VCSEL still not successfully fabricate to date. Thanks to have the technology to grow light emitting device with resonant cavity characteristics, so we can study the fabrication process of VCSEL-like device. Fabrication process and technology of GaN surface light emitting devices were studied in this thesis. A 3λmicro-cavity structure was considered both in devices characteristics and process needed. In the device structure, chosen the best one to achieve GaN VCSEL : intra- cavity structure with top dielectric DBR and bottom epi growth DBR. Device bottom DBR adopted AlN/GaN materials which can also reach high reflectivity under fewer DBR pairs due to higher index different between AlN and GaN. Device top DBR adopted SiO2/TiO2 dielectric materials which already have good coating technology around 410 nm wavelength to reach high reflectivity more easily. Due to intra-cavity and mirco-cavity, the fabrication process was more difficult than conventional light emitting device. The control of precise etching depth and the confined of current injection were needed. And in the lift-off process of top dielectric DBR : photo-resister will stick on sample surface in high temperature coating environment, so we suggested LOR solution to displace photo-resister to bear high temperature and successfully accomplish lift-off process. The EL wavelength of the GaN-based surface light emitting device was located at 410.6 nm with FWHM 7.4 nm and the cavity quality factor Q about 55.5. By increasing the injected current density, the EL wavelength has slightly red shift effect due to resonant cavity F-P dip.