Long Wavelength Vertical Cavity Surface Emitting Laser Grown by Metal Organic Chemical Vapor Deposition

• Main Author: 盧廷昌
• Other Authors: SC Wang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/77688102477397235854

博士 === 國立交通大學 === 光電工程系所 === 92 === In this study, we have developed the process for fabrication of long wavelength vertical cavity surface emitting lasers (LW-VCSELs) by metal organic chemical vapor deposition (MOCVD). LW-VCSELs with emission wavelength ranging from 1.3 mm to 1.5 mm featuring circular-beam output, low production-cost, single longitudinal-mode operation, and possible integration of two-dimensional array are potentially suitable for light sources in fiber communication systems and in medium and short distance data transmission systems. However, the absence of high refractive index contrast in InP-lattice-matched materials impeded the development of 1.3-1.5 mm VCSELs. In addition, active layers with insufficient gain at elevated temperature, absence of natural oxidized current aperture and poor heat conductance in material systems for long wavelength range are problems in making LW-VCSELs. Therefore, we started this study from design and simulation to obtain appropriate gain materials for LW-VCSELs. We have determined InGaAlAs as the gain material and applied it into the conventional edge emitting lasers to find out the optimized conditions of the active layers. The amount of compressively strain in quantum wells, the net amount of strain in multiple quantum wells (MQWs) with more pairs, and the impurity concentration strongly influenced the performance of edge emitting lasers. The overall optimization of these factors makes us obtaining low threshold current density of 1.4 kA/cm2. On the other hand, we have fabricated InP/InGaAlAs-based distributed Bragg reflectors (DBRs) with excellent electrical and optical properties using MOCVD and the growth interruption technique. Meanwhile, we have successfully fabricated, and demonstrated a rigid InP/airgap structure with high reflectivity at 1.54 mm using InGaAs as the sacrificial layer. The 3-pair InP/airgap DBR structure has a peak reflectivity at 1.54 mm with a stop-band width of about 200 nm. In addition, we have developed wafer-fusion technique to combine the conventional InP-based active layers with GaAs-based DBRs in order to simultaneously have the superior gain performance of InP-based active layers and the high reflectivity, high thermal conductivity and capability of oxidized layers of the GaAs-based DBRs. We demonstrated the optically pumped VCSEL structure with the fused bottom 30 pairs GaAs/AlAs DBR, InGaAlAs MQW and the fused top 25 pairs GaAs/AlAs DBR. The equivalent threshold current density is calculated to be 4 kA/cm2. The lowest threshold was obtained in InP-based LW-VCSELs. We successfully demonstrated the optically pumped InP-based VCSELs with the 35 pairs InP/InGaAlAs DBRs and 10 pairs SiO2/TiO2 top dielectric mirrors and a 2l thick cavity composed of periodic strain compensated MQWs to fully utilize the gain in every quantum well. The optically pumped VCSELs operated at room temperature with equivalent threshold current density calculated to be 2 kA/cm2. The wavelength of the output beam is 1562 nm. Although our goal to fabricate electrically driven continuous wave LW-VCSELs with single mode operation has yet to be fulfilled, this process has led to many other developments. For example, we have developed the MOCVD regrowth technique to fabricate buried tunnel junction devices and have applied this technique to fabricate long wavelength light emitting diodes with buried tunnel junction. At the same time, we have studied the quantum well inter-mixing effect, and the coexisting two-cavity configuration in conventional oxide confined VCSELs. All in all, basic physical phenomenon and material issues observed in this study will turn into useful information in making electrically driven LW-VCSELs in the future.