To investigate the high performance light source for high-speed plastic optical fiber (POF) communication application is important as high-speed short distance communication for the home networks becomes popular. It is straightforward to reduce the size of RCLEDs to increase the small-signal modulation bandwidth (f-3dB). But reduce the size of RCLEDs not only reduce the output power but also decrease lifetime because higher current density flowed through active region. In this paper, we improve. f-3dB of RCLEDs with the aperture of 84μm by reducing the number of quantum wells (QWs) in active region. We found the speed of RCLED inverse proportional to the number of QWs. By reducing the number of QWs to one, the device with standard aperture size exhibits high f-3dB as 235MHz at bias current of 20mA without sacrificing the other performance like maximum output power, high temperature performance, etc. These devices can transmit data rate as high as 500Mb/sec through graded-index POF over 50 meters. Beyond 1Gbits/sec, we have investigated red VCSELs as suitable high-speed light sources. The structure of red VCSELs is similar to RCLEDs except more pairs of DBR yield high reflectivity. Our red VCSEL can have output power as high as 1.5mW at 5mA and transmission data rate up to 2.5Gbits/sec.
Future in-house Multimedia networks, based on the IEEE 1394b standards, require low cost and robust optical
transmission system in the range of 100 meter. In this paper, we presented the state of the art 650 nm micro-cavity light
emitting diodes (RCLEDs) for such application. We had made RCLEDs with diameters of the emission window of 84, 60, 40μm for different requirements. Because of excellent epitaxy quality and structure design. Our RCLEDs perform record high power and efficiency. With expoxy encapsulated, the 84μm devices give an efficiency of 12% and yield more than 3.5mW at operation current 20mA. Our 40μm devices exhibit high small-signal modulation-bandwidths (f-3D) as 310MHz at bias current of 20mA. The output power of 40μm devices is still as high as 1.5mW, which is suitable for IEEE 1394b s400 standard. On the other hand, we had developed metal bonding RCLEDs (MBRCLEDs) to improve the high temperature performance of RCLEDs. By proper design the structure and process, the MBRCLEDs can have very low power decay as 0.6dB from 20°C to 100°C.
We have successfully developed a selective surface coating technique to control the modal behavior of the ionimplanted vertical cavity surface emitting laser. Using selective deposition of germanium coating by lift-off process, we could spatially control the threshold gain condition of the VCSEL to support the single transverse mode. The threshold current is 7 mA and single transverse mode operation is maintained up to 1 mW. The method is simple and nondestructive compared to other techniques.
Various metals were evaporated on the n-GaSb epilayer grown by low pressure metal organic chemical vapor deposition (MOCVD) to form the Schottky contact. The barrier height is almost independent of the work function and is determined entirely by the doping and surface property of the semiconductor. These results are in good agreement with Bardeen model. The carrier transport of Pd/n-GaSb contacts was studied and analyzed to discuss the effect of doping level of GaSb epilayer on the barrier height of the contact.