| Sb-based interband cascade lasers are among the effective sources of mid-IR radiation.AlSb/InAs/GaInSb/InAs/AlSb“W”type quantum wells were used as the active region for this type of lasers.The wavelength can be modulated by varying the thickness of the InAs and GaInSb layer.InAs/AlSb multi-quantum wells were used as the injection region to realize the recycling of carriers in each cascade stage.These designs enable interband cascade lasers with high efficiency,low threshold,and low power consumption.Currently,the interband cascade lasers have demonstrated excellent performance in the mid-IR region.This dissertation focus on the fabrication and characterization of Mid-IR interband cascades.Besides,a new physical phenomenon proposed by R.Yang named quantum real space transfer is also studied and verified preliminary.The main contents are listed as follows:1.Structural calculation of the interband cascade lasers.The band diagram of the active region is calculated by solving simplified Kane two-band model and one-band model with MATLAB programming.The results are basically consistent with the results simulated by Kane four-band model and results reported in the literature.Thus the feasibility of the simplified model is proved.In addition,the optical intensity of the waveguide is simulated by finite element method.2.Fabrication and characterization of the mid-IR interband cascade laser.High quality InAs-based interband cascade lasers material was grown on InAs substrate using a molecular beam epitaxy apparatus.The full width at half maximum of the minus first diffraction satellite peak is only 28.8’’,and the actual thickness of the cascade region is only 0.35%from the design value.The grown material was fabricated into ridge waveguide laser bars.The performance of the devices was carried out on a home-made set-up using a mercury cadmium telluride detector.The fabricated devices can lase at temperature up to 275 K and 226 K under pulsed and CW operation mode,respectively.The emission wavelength red shifted from 3.8μm at 80 K to 4.14μm at 275 K,with a threshold current density around 17 A/cm2 at 80K.Finally,the self-heating effects of narrow ridge devices were analyzed by comparing the threshold current density under different operating mode.It shows that when the temperature of heatsink is higher than 200 K,the self-heating effect will become the main factor limiting the device to operate at room temperature.The gold plating and epi-side down mounting can effectively improve the heat dissipation performance and alleviate the influence of self-heating effect on device performances.3.The internal optical loss of the device is characterized and analyzed.The loss of board area device and narrow ridge device were carried out by the cutback method and the Hakki-Paoli method,respectively.The value of loss of narrow ridge device varies from 14 cm-1 at 80 K to 20.3 cm-1 at 200 K,and 23.cm-1 at 220 K.For board area devices,the value of loss raises linearly from 8.1 cm-1 at 80 K to 16.2 cm-1 at 200K,and rapidly raised to 20.9 cm-1 at 210 K.The results show that the loss of the narrow ridge devices is larger than board area devices,which may be attributed to the sidewall effect of the narrow ridge device.Sidewall effects might be mitigated by optimizing the device fabrication process.Furthermore,optimization of the waveguide structure and the cascade structure are effective ways to reduce the loss and further increase the maximum operating temperature.4.A new physical performance---quantum real space transfer（QRST）is carried out on Sb-based heterostructure.Firstly the traditional real space transfer（RST）effect is studied on the GaAs/AlGaAs double quantum wells structure.The negative resistance effect is successfully observed with a threshold electric field of 1.5 kV/cm.Based on this research,the concept of QRST is studied.High-quality QRST materials were grown.After a series of processes,the QRST effect is initially observed based on InAlAs/GaAsSb step quantum wells.The voltage-current curve obtained on device agrees well with the simulation results. |
