Research On Ⅰ-Ⅴ Characteristics And Optical Spectrum Of Quantum Dot Lasers

Semiconductor quantum dots are important for basic physics studies and innovative opto-electronic device applications due to their discrete energy levels like a single atom. Studies of quantum-dot material growth and device applications have attracted immense interests of worldwide research groups. The samples with different thickness of InAs were grown by gas-source molecular beam epitaxy (GSMBE) on the InP substrate. Ridge waveguide lasers with different cavity length were processed using conventional semiconductor fabricating process and the characterizations of the lasers were preformed. The main results achieved in this work could be summarized as following:1.The development history of semiconductor lasers, both in domestic and aboard, are briefly given. Furthermore, the energy band of low-dimensional materials has been analyzed to indicate its advantages to manufacture photoelectric devices. The emission wavelength of InAs/InP quantum dot laser diode is in one of the low loss windows of optical fiber communication-1.55μm. Consequently, it often acts as optical-electric device and has potential application in the communication field.2. Ridge waveguide width of 6,8,10 and 12μm were successfully fabricated though optimizing device structure and related fabrication process. The laser was isolated by the material of Si3NX with thickness of 250 nanometers. The p-type and n-type contact of InP were the alloy of Ti/Pt/Au and Ge/Au/Ni/Au with the annealing temperature of 340℃.3.The I-V characteristics of InAs/GaAs double-hetcro (DH) structure QD laser diode are measured. Under low current condition, the relation ln /and the applied voltage is a straight line.By fitting ln(I) vs.V curves at different temperatures, the intercepts LnI0are obtained. Lnlo versus temperature are approximately linear relationship with a slope indicating -Eg/Κ, which can be used to measure the forbidden energy gap in GaAs QD laser. However, under large current condition, the InIversus V curves deviate from linear relationship but the I-V curves of the laser diode tends to operate as a resistance. In addition, these I-V curves can be used to fit the temperature coefficient of forward voltage, which is an important parameter used to measure the junction temperature of the laser diode.4. Two peaks of lasing emission were observed simultaneously from the laser diode with the cavity length of 1.5mm at 20℃. Multimode lasing starts with central wavelength at 1578nm. On this phenomenon, it was queried that whether the two peaks would make the laser be distinct from the one peak state and result in operating with two symmetric ellipse light spots rather than single in far-field pattern. We simulated the result according to Gaussian distribution and measured the far-field patterns by experimentation simultaneously. However, both of the two methods disaffirm the query and prove that its far field divergence angles still keep the TE00q mode and having one maximum value.Moreover, the InAs/InP QD laser far field divergence anglesθ∥×θ⊥are about 15°×43°on full-width at half-maximum (FWHM), which is just agreement with our computation result.5.Spectrum of quantum dot laser is very important and of great significance, as it can provided with mode characteristics, distribution of optical intensity at different frequency, tunable span, coupled mode phenomena between adjacent quantum dots etc. Based on weak and strong of applied current, spectrum is generally divided into fluorescence and simulated emission parts. With increase of applied current, the lasing peak tends to shift to shorter wavelength, such as, the InAs/GaAs quantum dot laser is with speed about 0.006nm/mA. However, the lasing peak usually shifts to higher wavelength during increasing operation temperature. InAs/InP quantum dot laser with lasing wavelength insensitive to operation temperature are demonstrated. Very high wavelength stability of 0.1035nm/K at the temperature range of 20℃to 60℃is obtained, which is only 1/5 times of the quantum well laser with wavelength stability of 0.54nm/K.