Browsing by Author "Su, Po-Yuan"

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Numerical Study on Optimization of Active Layer Structures for GaN/AlGaN Multiple-Quantum-Well Laser Diodes
(2008-09-01)
Chen, Jun-Rong
;
Ko, Tsung-Shine
;
Su, Po-Yuan
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
Theoretical analysis for different active layer structures is performed to minimize the laser threshold current of the ultraviolet GaN/AlGaN multiple-quantum-well laser diodes by using advanced device simulation. The simulation results show that the lower threshold current can be obtained when the number of quantum wells is two or three and the aluminum composition in the barrier layer is about 10%-12%. This result is attributed to several different effects including electron leakage current, nonuniform carrier distribution, interface charge density induced by spontaneous and piezoelectric polarization, and optical confinement factor. These internal physical mechanisms are investigated by theoretical calculation to analyze the effects of quantum-well number and different aluminum compositions in barrier layer on laser threshold properties. Furthermore, the effect of quantum-well thickness is discussed as well. It is found that the optimal quantum-well thickness is about 3 nm due to the balance of the advantages of a large confinement factor against the disadvantages of significant quantum-confined Stark effect (QCSE).
Numerical study on optimization of InGaN multi-quantum-well laser diodes with polarization-matched AlInGaN barrier layers
(2009)
Chen, Jun-Rong
;
Ko, Tsung-Shine
;
Su, Po-Yuan
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
The optical properties of InGaN multi-quantum-well laser diodes with different polarization-matched AlInGaN barrier layers have been investigated numerically by employing an advanced device simulation program. The use of quaternary polarization-matched AlInGaN barrier layers enhances the electron-hole wave function overlap due to the compensation of polarization charges between InGaN quantum well and AlInGaN barrier layer. According to the simulation results, it is found that among the polarization-matched quantum-well structures under study, lower threshold current and higher slope efficiency can be achieved simultaneously when the aluminum composition in AlInGaN barrier layers is about 10 similar to 15%. The optimal polarization-matched InGaN/AlInGaN laser diode shows lower threshold current and higher slope efficiency compared to conventional InGaN/InGaN laser diodes.