Abstract
Abstract Surface emitting light source now is regarding as a very important light source for many optoelectronic applications, such as high-speed LANs, computer links, optical interconnects, laser printing, display, optical mouse etc. In addition, the surface emitting light source can roughly be divided into two categories: surface emitting lasers and surface emitting LEDs. Among them, the mainstream is to develop vertical- cavity surface emitting lasers (VCSELs) and resonant-cavity light emitting diodes (RCLEDs) due to urgent need for optical communication. With respect to oxide-confined VCSELs, since the oxidized AlGaAs layer provides both excellent current and optical confinements, it gives rise to a reduced threshold current, a high efficiency, an enhanced modulation bandwidth, and a higher light output power as compared to other VCSEL structures. However, the oxide-confined VCSELs with a larger aperture (> 10 μm) would launch many higher-order transverse modes and exhibit the strong mode competition due to large refractive-index step, spatial hole burning, current crowding, as well as thermal effects. These effects would further degrade the performance of the devices with a large aperture such as the limits to the maximum light output power and the high frequency response. In order to overcome drawbacks mentioned above, we fabricate ring-shape VCSELs. These ring-shape VCSELs at room temperature exhibit a threshold current of 3.65 mA, a maximum light output power of 7.5 mW at 25 mA, and a differential resistance of 65 Ω. In addition, these devices exhibit a stable high-order-mode behavior over the entire operation current range resulting from the uniform carrier distribution and the weak mode competition. On the other hand, this TO-packaged 850-nm VCSEL for small-signal analyses shows a maximum modulation frequency of about 8 GHz corresponding to a modulation current efficiency factor (MCEF) of 2.47 GHz/mA1/2 and a clear and symmetric eye-opening feature at 10.34 Gb/s at 18 mA for both back-to-back and 66-m transmission test. These results ensure that the TO-packaged VCSELs can fulfill the OC-192 SONET mask-test. On the other hand, due to the continuously increasing demand for higher network capabilities of extending transmission distance at high data rates, it gives rise to the VCSELs toward launching longer wavelengths. A 1.3 μm VCSEL based on GaInAsN active layer would be the dominant candidate because it can be pseudomorphically grown on GaAs substrates by utilizing the well-established AlGaAs/GaAs distributed Bragg reflectors (DBRs). Besides, the relatively large conduction-band offset of GaInAsN/GaAs also exhibits a better high-temperature performance than that of InP-based material systems. Nonetheless, the large oxide-aperture VCSELs will tend to lase in high-order Laguerre-Gaussian modes at elevated current levels and leads to a problem in fiber coupling and result in the mode partition noise, which will further deteriorate the optical signal during data transmission. Attempts to control the mode dynamics that can be easily carried out by the following methods: surface relief (i.e. shallow etching technique) and anti-phase coating. Based on these two techniques, we have succeed in the 1.3 μm single-mode planar-type GaInAsN VCSELs with two Ga0.65In0.35As0.99N0.01 SMQWs as the active region grown by MOVPE. A circular surface relief and a thick silicon oxide was utilized to support the single fundamental mode and to planarize the VCSELs, respectively. The VCSELs with a 12-μm-diameter oxide-confined aperture and a 5-μm-diameter surface-relief aperture at room temperature exhibit a threshold current of 3 mA, a slope efficiency of 0.14 mW/mA, and a single-mode behavior. These VCSELs show a maximum light output power of 1 mW for the single fundamental mode with a transverse-mode suppression of more than 30 dB at the current level of 15 mA. Furthermore, the maximum operation temperature of the VCSELs is 90℃. Finally, the VCSELs also show a clear eye-opening feature and are well operated at 2.488 Gb/s under a bias current of 12.6 mA. These results confirm the 1.3 μm single-mode planar-type GaInAsN VCSELs have the potential capacity for fiber optic applications. On the other hand, the anti-phase coating VCSELs with four different diameters in Ge-coated apertures was formed in the center of the device to improve the characteristics of transverse mode. In addition, a thick silicon oxide film was used to planarize the VCSELs. The VCSELs with a 13-μm-diameter oxide-confined aperture and a 7-μm-diameter Ge-coated aperture at room temperature exhibit a stable single-mode behavior and a transverse-mode suppression of more than 35 dB over the entire operational range. In addition, nowadays, LED have been widely used in short-distance low-cost local area networks (LANs) over polymethyl methacrylate (PMMA) plastic optical fiber (POF), which exhibits the minimum attenuation rate in the 650 nm wavelength. Nonetheless, LEDs have typically an inherent low light extraction efficiency due to the existence of high difference in refractive index at the semiconductor-air interface so that only a few of the light is available to escape from the surface. One of particular interesting researches is focused on RCLED mainly because of the feasibility of increased extraction efficiency with micro-cavity structure. Based upon the demand of low-cost mass productions, we will propose an alternative method to realize the planar-type 650-nm RCLEDs by using silicon oxide. The device with a SiOx planarized layer exhibits a low operating voltage of 2.3 V at 20 mA, a maximum light output power of 304 μW at 15 mA, and the best external quantum efficiency of 3 % at 1.2 mA. In addition, the SiOx-planarized device shows emitting peak wavelength at 647 nm at 20 mA and exhibits less temperature sensitivity than that of their counterpart. The RCLED with a 30-μm diameter has the maximum 3-dB frequency bandwidth of 275 MHz at a driving current of 40 mA. Finally, the SiOx-planarized device also shows a clear eye-opening feature as operating at 100 Mbit/s at 20 mA.