Ghasem Alahyarizadeh | Universiti Sains Malaysia (original) (raw)

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Papers by Ghasem Alahyarizadeh

There are several equation sets that are used to characterize of the performance parameters of a ... more There are several equation sets that are used to characterize of the performance parameters of a quantum well (QW) lasers. One of simple and important equations groups which are used to study of laser characteristics in the almost powerful and expensive simulation tools such as Crosslight, ISE TCAD and SILVACO is of rate equations. A numerical analysis of rate equations is a powerful tool to study of carriers and photons behavior in the semiconductor lasers. The differential rate equations are used to estimate simulated and spontaneous emissions of laser in the all semiconductor simulation softwares [1-7]. A new visual and analytical model to study effects of structure parameters on laser performance of InGaN single quantum well lasers based on solving rate equations by using user friendly programming software, Delphi, is presented. This model has provided a graphical user interface (GUI) for researchers by which one can work directly with all laser parameters throughout the simulation work and analysis without the need to access source code[1]. We have investigated effects of different parameters such as quantum well thickness, separate confinement heterostructure (SCH) thickness and cavity length on the principle characteristics of the laser which include laser time response (P-t), and output power-current (P-I) characteristics. Meanwhile related features such as turn-on delay time of lasing, threshold current and slope efficiency have been investigated. Figure 2 shows the graphical user interface (GUI) of the main program, which uses to input parameters such as QW and SCH thickness and etc. Simulation results of P-I characteristics of InGaN SQW laser with our software has shown in figure 2. Also figure 3 shows the P-t characteristics of the simulated InGaN SQW laser. In conclusion, the presented work demonstrates a new visual, open source and analytical model based on solving rate equations by user friendly Delphi programming software. Our model in comparison wi- h other analytical software and expensive simulators provides directly access to the parameters of lasers throughout the simulation and analysis.

The performance characteristics of green InGaN multi-quantum well laser diode structures emitting... more The performance characteristics of green InGaN multi-quantum well laser diode structures emitting at 500 nm to 510 nm were investigated numerically. A threshold current of 87.2 mA corresponding to the threshold current density of 4.84 kA/cm 2 and a threshold voltage of 8.837 V were achieved for a basic structure emitting at 504.31 nm output emission wavelength. The effects of well numbers, well thickness, barrier thickness, and barrier doping on performance characteristics such as output power, threshold current, slope efficiency, and differential quantum efficiency were studied. The basic structure and material parameters used in the model were extracted based on the newest literatures and experimental works. Simulation results indicated that lowest threshold current, highest output power, differential quantum efficiency and slope efficiency are observed when the number of well layers is one and well thickness is between 3 and 4 nm. Significant changes in output power, threshold current, and slope efficiency were observed with the variations in barrier thickness and doping.

The effect of number of quantum wells and quantum well thickness on the optical performance of In... more The effect of number of quantum wells and quantum well thickness on the optical performance of InGaN vertical cavity surface emitting laser (VCSEL) was numerically investigated using Integrated System Engineering Technical Computer Aided Design (ISE TCAD) simulation program. The simulation results indicated that the output power and differential quantum efficiency of the double quantum well (DQW) laser were increased and threshold current decreased as compared to the single and triplet quantum wells VCSEL. Threshold current enhancement in the single quantum well (SQW) is attributed to the electron carrier leakage increasing from active layers because of the lower optical confinement factor. Simulation results show that in the double quantum well, the optical material gain and electron and hole carrier densities are approximately uniform with respect to the SQW and TQW. Also these results indicated that the electron current density in the DQW is the lowest. In the active region, electrical field decreased for the double quantum well because of the built-in electrical field reduction inside the quantum well. Finally the effect of quantum well thickness in DQW GaN-based VCSEL was investigated and it was observed that DQW VCSEL with 3 nm quantum wells thickness had the optimum threshold current.The simulation results indicate that the double quantum well GaN-VCSEL has a better performance as compared to the single and triplet quantum wells VCSEL.► The quantum well effects on the InGaN VCSEL performance were investigated. ► DQW InGaN VCSEL has a better performance as compared to the SQW and TQW VCSEL. ► InGaN VCSEL with the 3 nm QW thickness has the optimum threshold current.

The effect of built-in polarization on the performance characteristics of green InGaN single quan... more The effect of built-in polarization on the performance characteristics of green InGaN single quantum well (SQW) laser diode (LD) structures with ternary AlGaN or quaternary AlInGaN electron blocking layer (EBL) having the same bandgap energy, was investigated numerically. Simulation results indicated that using quaternary AlInGaN EBL effectively improves the performance characteristics of green InGaN SQW LDs. Using AlInGaN EBL significantly reduces the built-in polarization and fixed polarization charge densities at the EBL and the last InGaN barrier interface. Furthermore, using quaternary AlInGaN EBL increases the radiative recombination and decreases the non-radiative recombination in the well. The laser structure with AlInGaN EBL has lower threshold current, and higher output power, differential quantum efficiency (DQE) and slope efficiency compared with the laser structure with conventional AlGaN EBL.

The electrical properties of deep violet InGaNdouble quantum well (DQW) lasers emitting at 390 nm... more The electrical properties of deep violet InGaNdouble quantum well (DQW) lasers emitting at 390 nm have been investigated with varying cavity length from 250µm to 600µm using the Integrated System Engineering Technical Computer Aided Design (ISE TCAD) software. The simulation results indicated electrical properties of the violet InGaN DQW laser are strongly dependent on cavity length. They showed that the series resistance of laser system decreases by increasing cavity length. It causes increase in applied current to the laser system and increase in the output power consequently. The results also indicated that lasers with longer cavity length have higher electron current density and higher electron current leakage, consequently higher threshold current and lower performance.

An analytical, visual and open source model based on solving the rate equations for InGaN/GaN sin... more An analytical, visual and open source model based on solving the rate equations for InGaN/GaN single quantum well (QW) lasers has been carried out. In the numerical computations, the fourth-order Runge-Kutta method has been used for solving the differential rate equations. The rate equations which have been considered in this simulation include the two level rate equations for the well and separate confinement heterostructure (SCH) layers. We present a new and inexpensive modeling method with analytical, visual and open source capabilities to investigate and comprehend the QW laser characteristics such as time behavior of carriers in SCHs and QW, photon density, output power and gain, and also the output power versus current which presents the threshold current of the laser. The characteristics of the QW lasers, which include laser time response (P-t), turn-on delay time of lasing and output power-current (P-I) characteristic and related features such as threshold current and slope efficiency have been investigated. Our model accurately computes the P-t and P-I characteristics such as turn-on delay time, threshold current and slope efficiency, and also illustrates the effects of parameters such as the injection current and geometry.

The performance characteristics of a deep violet InGaN double quantum well laser diode (LD) such ... more The performance characteristics of a deep violet InGaN double quantum well laser diode (LD) such as threshold current (Ith), external differential quantum efficiency (DQE) and output power have been investigated using the Integrated System Engineering Technical Computer Aided Design (ISE-TCAD) software. As well as its operating parameters such as internal quantum efficiency (ηi), internal loss (αi) and transparency threshold current density (J0) have been studied. Since, we are interested to investigate the mentioned characteristics and parameters independent of well and barrier thickness, therefore to reach a desired output wavelength, the indium mole fraction of wells and barriers has been varied consequently. The indium mole fractions of well and barrier layers have been considered 0.08 and 0.0, respectively. Some important parameters such as Al mole fraction of the electronic blocking layer (EBL) and cavity length which affect performance characteristics were also investigated. The optimum values of the Al mole fraction and cavity length in this study are 0.15 and 400 μm, respectively. The lowest threshold current, the highest DQE and output power which obtained at the emission wavelength of 391.5 nm are 43.199 mA, 44.99% and 10.334 mW, respectively.