850 nm 面射型雷射布拉格反射鏡特性之模擬分析

Abstract

本論文利用ISE-TCAD已設計的850nm氧化侷限型結構，模擬元件結構摻雜濃度最佳化條件，而得n型DBR的摻雜濃度為 = 2.5x1O18 cm-3; p型DBR的摻雜濃度為 = 1x1O19 cm-3是最適當的。或許製程上的進步我們可以再提高摻雜濃度，但因電子電洞移動率及所造成的材料電阻率的差異，須保有 > 的前提。 因考慮降低串聯電阻、臨界電流的問題，故設計了漸變式(graded) 披覆層與張力（tensile strain）披覆層。從元件的L-I-V特性表現可見，當張力披覆層厚度大於10 nm 時元件即無法雷射(Lasing)，此應是量子穿隧效應的結果；而當張力披覆層厚度為3 nm 時，則有非常好的發光效率與臨界電流，此可證明張力披覆層的功效。 最後，我們模擬分析各種狀況的分佈型布拉格反射鏡(DBR)反射率。對於漸變式(graded) DBR而言，當中間層厚度為20 nm 以上時，DBR 就需要25對以上才能有與一般階梯式DBR一樣的反射率水準。若 DBR 各層厚度有+/- 1%誤差度，只要有25對以上的DBR，其截 止帶( stop band )宽度即夠大，而在850 nm 處的反射率值也幾乎不受影響。另外以矩陣光學為基礎，我們進一步分析DBR對非正向入射光的反射率，在 45º 的入射角下，形成建設性干涉的光的波長約縮短約20 nm。

In this thesis work, we simulated and analyzed the optoelectronic properties of 850 nm oxide-confined vertical-cavity surface-emitting laser (VCSEL) diodes using ISE-TCAD simulation software. For the optimized characteristicsof VSCELs, n type DBR doping concentration = 2.5x1O18 cm-3 and p type DBR doping concentration = 1x1O19 cm-3 .Even thought we can increase the doping density in the advantage process, still need to follow > are expected. Considering the resistance and threshold current concerns of VCSELs, we simulated the graded and tensile strain cladding layers. Judging from the L-I-V characteristics, we found the fact that the thicker tensile-strain cladding layer greater than 10nm may prohibit the device from lasing. And the 3 nm-thick tensile-strain cladding layer can give low threshold currents and high lasing efficiency of VCSELs. Furthermore, we simulated the optical reflectance of various DBR structures. In the graded DBRs, when the thickness of the graded layers are over 20 nm, 25 pairs more DBR structures can give the same reflectance of regular abrupt DBRs. As the thickness of DBR layers are in 2% variation, processes, 25 pairs more DBR structure can also provide the same reflectance values of non-variant DBRs at the main wavelength and applicable stop-band width. Finally we utilized the matrix optics to analyze the effects of pair numbers and light incident angle on the reflectivity spectra of DBR. For the case of 45º incident angle of light ,the resonant wavelength shift about 20 nm.