Simulation And Design Of Multiple Wave-band Quantum Cascade Laser

Quantum cascade laser(QCL)is a special luminescent unipolar semiconductor device composed of the coupled multiple quantum wells operating with the tunneling transports and intersubband transitions of the injected carriers,which is designed by band by energy-band engineering and quantum tuning technologies.The emission wavelength of QCL,which has so far been extended from mid-infrared to terahertz,can completely specified and accurately modified by the thicknesses of quantum wells,thus free from the energy band-gap of the constituent semiconductors.Compared with the electron-hole recombination mechanism of ordinary semiconductor lasers,the repeatedly tunneling carriers could be duplicated for intersubband transitions in the multiple cascade structure,leading to a great amelioration of the lasing efficiency applied prospectively for future optoelectronics.In the present study,a numerical model used for evaluating electronic scattering between the restricted energy levels(RLS)is established specially for the basic structure of quantum cascade lasers to accurately calculate lasing performances in optimization designs.The optical-gain,current-threshold and injection-efficiency models are individually deduced from the general velocity model to be applied for calculating electronic levels,threshold of particle reversal,reversal particle number at steady state,threshold current,laser gain coefficient and injection efficiency.Conforming to the operation characteristics of QCL,a short-range injection structure is designed to reduce the thermal scattering of injected carriers and thus improve the long-wave lasing gain and operating temperature.RLS is combined within the QCL device simulations to analyze the electron distribution,leakage current,laser spectrum,transmittance and L-I-V curves.As the temperature increases,the number of electrons in the upper energy level of the modeled QCL laser decreases from 70%of free-carriers to 27%,and the lasing photon energy is abated to 32 me V.Based on resonance tunneling and auxiliary scattering,a multi-level hybrid extraction/injection structure is designed and simulated as a QCL device with Ga As/Al_0.17Ga_0.83As quantum wells in active region,which increases the peak value of particle number inversion by 44.53%.A laser model is constructed by using the ideal barrier contour and the actual barrier contour respectively.It is indicated that the J-V curves represent well consistency under bias below threshold,while the obserble difference will arise when beyond threshold,which is primiarily attributed to discrepancy of potential distributions between actual and ideal barriers.For the long wave QCL with the multi-level hybrid extraction/injection source,no leakage current appears at the temperature up to 260 K(characteristic temperature),implying that the effective suppression on leakage current and the improved stability of electrical currents before threshold have been acquired for higher injection efficiency and working temperature.