氮化鎵面射型發光元件的製造與光學特性

Abstract

氮化鎵垂直共振腔發光元件(RCLED)由於磊晶技術上的困難，以致於難以獲得高品質的共振腔。本實驗室具有成長共振腔特性發光元件之技術，並進行元件光特性實驗及製程之研究。 本論文主要研究氮化鎵面射型發光元件之光激發特性及製程相關技術，第一部份將進行光激發特性實驗之研究，第二部份將實際製作RCLED並討論其特性，RCLED元件設計為採用3λ微共振腔腔長，此設計能兼顧元件特性與製程之需求。元件結構上為採用目前最有機會成功製造藍光面射型發光元件的內部共振腔(Intra-cavity)形式的結構:下層DBR反射鏡採用氮化鋁(AlN)與氮化鎵(GaN)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(SiO2)與二氧化鈦(TiO2)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。 在第一部份中，我們籍由光激發觀察到本實驗已可以將DBR的dip設計在MQW的發光波長上，計算出共振腔的品質因素Q為113，output power增加1.6倍。 在第二部份元件製程方面，由於採用內部微共振腔結構，所以在蝕刻深度的控制及電流侷限的設計上，都較一般發光元件困難。電激發面射型發光元件，其電激發波長位於420 nm、半高寬為4.3 nm。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 light emitting diode (RCLED) acknowledged basic difficulty is in in-situ epitaxial growth technology to form high quality resonant cavity. Thanks to have the technology to grow light emitting device with resonant cavity characteristics so that we can study the exam for optical characteristics of the device and fabrication process of VCSEL-like device so as to accumulate the experience in GaN RCLED. Fabrication process and technology of GaN surface light emitting devices and optical pumping were studied in this thesis. In the first section, exam for optical pumping will be done; in the second section, using real structure to make RCLED. A 3λmicro-cavity structure adopted by above device design 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. In the first section, by the exam of optical pumping，we observed the dip of DBR could be designed for MOQ’s EL wavelength, the quality factor “Q” is 113, and the status of power increasing was discovered. In the second section for fabrication process of device, due to intra-cavity and micro-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. The EL wavelength of the GaN-based surface light emitting device was located at 420 nm with FWHM 4.3 nm. By increasing the injected current density, the EL wavelength has slightly red shift effect due to resonant cavity F-P dip.