850nm高速和光子晶體面射型雷射之特性量測與分析

Abstract

本論文針對砷化鎵之面射型雷射(VCSEL)分成兩部分來探討，第一部分對於面射型雷射(VCSEL)在進行離子佈植製程後，對於不同氧化層之氧化型面射型雷射高速特性影響進行研究分析，並逐一建立元件結構之等效電路模型來進行模擬比對，第二部分對於氧化型和離子佈植型的光子晶體面射型雷射(VCSEL), 從光子晶體雷射的L-I曲線、輸出頻譜、近場發光圖形以及發散角等對光子晶體雷射做詳細的探討。 研究的850nm VCSEL，其磊晶結構為上及下反射層分別由22及39.層Al0.15Ga0.85As / Al0.9Ga0.1As構成，主動層為GaAs / AlGaAs多重量子井，氧化層Al0.98Ga0.02As成長於主動層上三層處。在高速特性量測方面，完成建立兩晶圓級之量測系統，可在製程之後直接點測元件的高速特性，以避免封裝對於元件造成調變速度限制。 首先我們探討尖細型氧化層讓電流孔徑小於輸出光孔徑而且也讓衰減率也進而變小兩倍進而提升調變速度.論文首先以普遍製作高速元件之氧化型VCSEL一比較實驗。實驗量測結果顯示，在同樣氧化孔徑5.5 μm下，一般氧化結構之VCSEL與尖細型氧化結構之VCSEL，其調變速度分別為9.5及13.2 GHz。接著尖細型氧化結構之VCSEL擁有清晰的眼狀圖( eye diagram )其下降時間為 26 ps,上升時間為 40 ps 而抖動也小於 20 ps. 接著根據不同的VCSEL結構，建立一等效電路模型，以Agilent ADS程式進行模擬，分析元件結構中等效RC對高速調變的影響。由等效電路的分析模擬，可以更清楚瞭解元件結構影響高速特性的程度，進而改進元件製程，以期能製造出更高速的VCSEL。 最後我們探討(邊模抑制比 SMSR)>40dB之高輸出功率( >1 mW)單一模態離子佈植光子晶體面射型雷射(PC-VCSEL).此光子晶體面射型雷射擁有非常低的臨界電流為1.25mA, 其氧化孔徑為10 μm. 由實驗結果可知, 使用離子佈植當作電流侷限和光子晶體當作輸出光侷限可製作出高輸出功率單一摸態的面射型雷射.而相同的概念也將會在未來逐漸被應用在1.3 μm面射型雷射上.

This thesis presents our study on GaAs based vertical-cavity surface-emitting laser (VCSEL) and is divided into two parts. The first part discuss the improvement of high speed performance of oxide VCSEL by utilizing tapered oxide layer. We setup wafer-level high speed measurement system which allows us to test device immediately and avoids parasitic effect from package. The damping rate from the modulation response was found to reduce two times in the tapered oxide VCSEL and therefore enhanced the maximal modulation bandwidth. With same oxide aperture size 5.5 μm, tapered oxide VCSEL shows better modulation bandwidth of 13.2 GHz while blunt oxide VCSEL has 9.5 GHz. A very clean eye was demonstrated from improved VCSEL with rising time of 26 ps, falling time of 40 ps and jitter of less than 20 ps, operating at 10Gb/s with 6mA bias and 6dB extinction ratio. We also build an equivalent circuit model to analyze the bandwidth limitation affected by VCSEL intrinsic impedance. The simulation results could make the modulation limitation clearly and help us to modify the VCSEL process for high speed operation.

In the second part of the thesis, we report a high power (>1 mW) singlemode proton-implanted photonic crystal vertical-cavity surface-emitting laser (PC-VCSEL) with high SMSR (> 40 dB) throughout the whole operation current range. This PC-VCSEL, with an aperture of about 10 μm, has ultra-low threshold current of about 1.25 mA. We analyze the L-I curve, emission spectra, near field pattern, divergence angles of photonic crystal VCSELs fabricated with oxide-confined and implant structure. The present results indicate that a VCSEL using proton implantation for current confinement and photonic crystal for optical confinement is a reliable approach to achieve high-power singlemode operation of a VCSEL. This concept will be applied to a 1.3μm VCSEL and other commercial applications in the future.