High Gain, Low Threshold Current GaInAsP Based Vcsels for Operation at 1.24UM
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HIGH GAIN, LOW THRESHOLD CURRENT GaInAsP BASED VCSELS FOR OPERATION AT 1.24UM Zhuopeng Tan, Yixin Li, Aris Christou Department of Materials Science and Engineering University of Maryland, MD 20742
Abstract: An electrically pumped 1.24um GaxIn1-xAsyP1-y Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and simulated. Threshold gain of 153cm-1 and threshold current of 1.00mA was obtained. The external efficiency predicted is 0.31. Also the optimized design of VCSEL structure is presented in this article. GaInAsP and AlInAs constitute the Distributed Bragg Reflectors (DBRs) multilayer stack. Reflectivity of the top DBRs is 0.97 and reflectivity of the bottom DBRs is 0.9978 and is shown to provide a good resonant cavity and sufficient lasing intensity. Compared with other reported structures, the present VCSEL has a lower threshold current and higher threshold gain.
Index Terms: VCSEL 1.24um, GaxIn1-xAsyP1-y, high threshold gain.
1.INTRODUCTION VCSEL is a semiconductor laser diode that emits light in a cylindrical beam vertically from the surface of a fabricated wafer. It offers significant advantages, such as low electric power consumption, capability of on-wafer testing etc., compared to the edgeemitting lasers currently used in the majority of fiber optic communications devices. VCSEL can be fabricated efficiently on a semiconductor wafer. Even more important, the ability to manufacture these lasers using standard microelectronic fabrication method allows integration of VCSELs on-board with other components without requiring prepackaging. As an enabling technology, VCSEL allows superior new systems and products to be created at a lower cost [1,2,3]. The device investigated here is mainly composed of 10 layers Multi-Quantum-Well (MQW) and many distributed bragg reflector (DBR) layers on either side of the MQW. Here is the schematic of the device:
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2.THOERETICAL CONSIDERATOINS Structure Design The designed wavelength of the VCSEL is 1.24um. That means Eg=1.00eV for the active layers. With the help of x(1 − x)[(1 − y ) E ABD ( x) + yE ABC ( x)] + y (1 − y )[(1 − x) E BCD ( y ) + xE ACD ( y )] E g ( x, y ) = x(1 − x) + y (1 − y ) and EABC(x)=xEAC+(1-x)EBC-x(1-x)bpABC [4] for ternary alloy AxB1-xC, Ga0.57In0.43As0.90P0.10 was chosen as the active layer material. Where bpABC is bowing parameter [2], Table 1 Bowing parameters and binary alloy energy band gap bpGaInP=0.758eV Eg(InP)=1.344eV bpGaInAs=0.4eV Eg(GaAs)=1.424eV bpInAsP=0.36eV Eg(InAs)=0.354eV bpGaAsP=0.186eV Eg(GaP)=2.78eV bpAlInAs=0.74eV Eg(AsAs)=2.16eV Use the same way, Ga0.40In0.60As0.54P0.46 was selected as barrier material to form QW with Ga0.57In0.43As0.90P0.10, and the difference between them is 0.20eV(See Table 2 for the other parameters). There are 10 active layers and 9 barrier layers with thickness of 8nm and 10nm for each layer respectively. As Al is very easy to be oxidized, and from Koley’s experiment [5] we knew that the oxidation rate decreases significantly after some time for it greatly depends on the concentr
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