1.3μm n-type modulation-doped strain-compensated multiple quantum well (MD-SCMQW) AlGaInAs/AlGaInAs laser diodes

• Main Authors: Po-Hsun Lei, 雷伯薰
• Other Authors: Meng-Chyi Wu
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/29086756741135323324

博士 === 國立清華大學 === 電子工程研究所 === 91 === 1.3 and 1.55 μm semiconductor laser are most popular for the application in subscriber networks and optical interconnection systems. 1.3 μm-based semiconductor lasers have lower dispersion but higher attenuation compared to that of 1.55 μm-based semiconductor lasers. Besides, one of the most troublesome components in present laser modules is a thermoelectric cooler, which both makes the modules expensive and complicated but also may degrade its long-term reliability. In order to overcome these problems, 1.3 μm high power and without thermoelectric cooler AlGaInAs with high conduction band offset than conventional GaInAsP are used as light source in optical interconnection systems. The higher conduction band offset can alleviate the Auger recombination that will affect the performance of long wavelength laser diode so that increase the light output power. In this thesis, we first investigate the 1.3 μm AlGaInAs/AlGaInAs strain compensated multiple-quantum well. The compress strain wells which have several merits in optical and reduction of threshold current and compensated by tensile barriers to increase the well number. The threshold current density and differential quantum efficiency for the as-cleaved BA LDs with a 900 μm cavity length are 400 A/cm2 and 22%, respectively. We also calculate the internal quantum efficiency, internal optical loss, and threshold gain as 54.1%, 6.5cm-1, and 45 cm-1. The characteristic temperature of 75 K between 20 and 80 ℃, and the longitudinal mode oscillation has a red-shift rate of 0.5 nm/℃ under 25 ℃ and 60 mA. Graded index separate confinement heterostructure (GRINSCH) has superior optical confinement and smooth electric field intensity distribution than that of step (or abrupt) structure. Besides, to tailor the electric field intensity distribution in the abrupt junction between InGaAs and InP, we introduce a thin graded composition (GC) GaInAsP layer between InGaAs and InP. With the GC GaInAsP layer, the 3μm-ridge-stripe LDs without facet coating under the CW operation exhibit a lower threshold current of 14 mA, a lower resistance of 7.8 Ω, a higher differential quantum efficiency of 47.46%, a higher characteristic temperature of 79 K in the range from 20 to 80 ℃and 42 K in 80 to 100 ℃, and a red-shift rate of 0.43 nm/℃, which are better than those of the LDs without the GC GaInAsP layer. The differential gain for LDs with GC GaInAsP layer is about 8.45x10-16 cm2 for 300-μm cavity length and decreases to 4.68x10-16 cm2 for 900 μm. The relaxation oscillation frequency is about 9.2 GHz under the 80 mA driving current at 20℃. With neglecting the effect of damping factor and couple loss, the calculated 3-dB frequency width can reach to 14.26 GHz under the 80 mA driving current at 20℃. More recently, modulation doping in the barriers will serve several merits such as lower transparency carrier density and higher optical gain. The BA LDs with this optimum concentration of 5 x 1018 cm-3 in the doped barriers exhibit the threshold current density, internal quantum efficiency, internal optical loss, threshold gain (for the cavity length of 300 μm), and transparency current density of 215 A/cm2, 61.7%, 7.5 cm-1, 47.5 cm-1, and 71 A/cm2, respectively, which are much better than those of the LDs with undoped and other doping concentrations in the barriers. In addition, the ridge-stripe LDs without facet coating have a lower threshold current of 12.5 mA, an enhanced differential quantum efficiency of 52.3%, a characteristic temperature of 85 K in the temperature range from 20 to 80 ℃, and a red-shift rate of 0.38 nm/℃ under the CW operation. The relaxation oscillation frequency with driving current of 80 mA under 20 ℃ is about 9.9 GHz. Without consideration to damping factor and couple loss, the calculated 3-dB bandwidth is about 15.34 GHz. InAsP/InP/InGaP MQW has higher conduction band offset than that of GaInAsP MQW. In this thesis, InAsP/InP/InGaP with n-type doping laser diode is also investigated. The optimum doping concentration is 1x1018 cm-3 in the Si-doped barrier and InP intermediate layer. The threshold current density can be reduced to 0.8 kA/cm2 for 900-μm-cavity length for these optimum thickness and doping concentration. In addition, the LDs exhibit an enhanced differential quantum efficiency of 25% and an internal quantum efficiency of 31%. The internal optical loss can be also lowered to 19.01 cm-1. The threshold gain will be reduced to 43.07 cm-1 compared to 44.1 cm-1 for the LDs with undoped active region.