850nm面射型雷射之高速特性量測與分析

Abstract

本論文針對砷化鎵(GaAs)之面射型雷射(VCSEL)，在進行離子佈植製程後，對於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。研究的850nm VCSEL，其磊晶結構為上及下反射層分別由22及32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，完成建立一晶圓級之量測系統，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。 由於離子佈植為簡易且有效降低元件寄生電容的方式，本論文以普遍製作高速元件之氧化型VCSEL做一比較實驗。實驗量測結果顯示，在同樣氧化孔徑8µm下，只有氧化結構之VCSEL與經過離子佈植製程後之VCSEL，其調變速度分別為2.3及8.4 GHz。接著在相同離子佈植條件下，改變氧化孔徑大小為6、7、8µm，量測得其調變電流效率係數(MCEF)分別為3.06、5.54及5.96 GHz /mA1/2。 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(modeling)，分析元件結構等效RC電路對高速調變的影響。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。

This research is focusing on the study of high speed modulation characteristics of GaAs base vertical cavity surface emitting laser (VCSEL) with oxide-confined and oxide-implant structure, and establishes an equivalent circuit model for electrical characteristic analysis. The 850nm VCSEL structure consists of GaAs /AlGaAs multi-quantum-well. Top and bottom distributed bragg reflector has 22 and 32 pairs Al0.15Ga0.85As /Al0.9Ga0.1As respectively. We setup an on-wafer high speed measurement system which benefits us to test device immediately and avoid modulation limitation from package. Proton implant process is a simple method to reduce parasitic capacitance. For this, we fabricate oxide-only and oxide-implant VCSEL and compare with their modulation characteristics. With same oxide aperture size 8µm, oxide-implant VCSEL has better modulation bandwidth 8.4 GHz and oxide-only VCSEL has 2.3 GHz. Then we compare oxide-implant VCSEL with different oxide aperture size as 6, 7 and 8µm, and obtain modulation current efficiency factor (MCEF) as 3.06, 5.54 and 5.96 GHz /mA1/2 respectively. We build an equivalent circuit model, corresponding different VCSEL structure, for modeling the modulation limitation, affected by RC circuit, and simulate circuit by Agilent Advanced Design System software. The simulation results could make the modulation limitation clearly and help us to modify the VCSEL process for high speed operation.