The Structure Optimization And Fabrication Of 1.3μm Strained-Layer Multiple-Quantum-Well Lasers And Optical Amplifiers

Being the optoelectronic devices widely used in optical communications, long-wavelength semiconductor lasers are required to have as low as possible threshold current and eminent temperature characteristics for low cost and uncooled operation at elevated temperatures. Semiconductor optical amplifiers (SOA) cannot be replaced by optical-fiber amplifiers in the applications of signal processing. However, the overall performances of SOAs have to be improved for the extensive applications. The structures of 1.3μm InGaAsP/InP strained-layer multiple quantum-well lasers (SL-MQW) and SOAs were optimized and high performances were realized. The important results are as follows.Theoretical results: 1) For only one quantized energy level for conduction band electrons in the quantum wells, the maximum band gap of barrier layers decreases with increased well width. The transparency carrier density decreases with the reduced hole effective mass in the valence band. The appropriate strain amount and well width produce not only enhanced gain coefficient but also reduced transparency carrier density. The differential gain coefficient decreases with increased sheet carrier density. 2) For as lowest as possible threshold current, the optimum stripe width is about 1.3μm and 2 urn in buried heterostructure (BH) and ridge waveguide structure (RWG) MQW lasers, respectively. The optimum cavity length or well number in narrow stripe structure is enhanced by a factor of 1.8 compared to that in broad area structure. The minimum threshold current could be less than 1 mA when the facet reflectivity is 0.9. 3) The expression derived by the author shows that characteristic temperature of threshold current is determined by the characteristic temperatures of transparency current density and external differential efficiency, where the former one is determined by the radiative recombination efficiency, the later one by the electron leakage in the conduction band at elevated temperatures.Experimental results: 1) Increased well number has improved the temperature characteristics of threshold current and external differential efficiency. The discrepancy of threshold current characteristic temperature between theory and experiment doesn't exceed 8%. 2) An undoped AlInAs layer with 18 run thickness effectively suppresses the electron leakage in the conduction band from the MQW active region to P-type doped InP cladding layer, the power penalty is -2.2 dB with a drive current of 60 mA. The InGaAsP/InP MQW lasers have qualified the requirement of the uncooled operation at high temperatures. 3) The optimized structure of InGaAsP/InP tensile strained MQW is: tensile strain amount 1%, well width 10.5 nm, barrier thickness 18 nm, well number 3, band gap wavelength of barrier layer 1.15μm, The threshold current at room temperature in the RWG MQWlaser is 13 mA, the external slope efficiency per as-cleaved facet is 0.29 mW/mA. 4) The structure of 1.31 urn SOA is as: the active region of alternatively grown 4 compressively strained QW and 3 tensile strained QW, 7o tilted RWG, transparent buried window facet, anti-reflectivity coating on both facets. The SOA module performances are as: fiber-to-fiber gain 25 dB, gain bandwidth 56 nm, polarization dependent gain o.6 dB, noise figure less than 8.8 dB in the wavelength of 1280 - 1340 nm, saturated output power 14 dBm. The high performances are on the advanced level among the SOAs in the world.