Jy-Wang Liaw

Light-induced negative differential resistance in planar InP/InGaAs/InP double-heterojunction p-i-n photodiode

Negative differential resistance (NDR) was observed in the dc photocurrent-reverse bias characteristics at 1.55 μm wavelength of a planar InP/InGaAs/InP double-heterojunction p-i-n photodiode, which is designed for high-speed operation. In the bias range of measurements, two NDR regions can be observed, which are suggested to be mainly caused by the drop of average electron velocities in both the InGaAs absorption and InP buffer layers, i.e., the transferred electron effect. For providing evidence, power dependence of these NDR regions was investigated. Besides, another high-responsivity p-i-n photodiode was fabricated and characterized for comparison.

Effectiveness of the pseudowindow for edge-coupled InP-InGaAs-InP PIN photodiodes

We have shown that edge-coupled PIN photodiodes can benefit from the incorporation of a pseudowindow of appropriate thickness. In our experiments, a pseudowindow 2-3 /spl mu/m thick can effectively protect the device and antireflection (AR) coating during the cleavage process without sacrificing the device efficiency and speed performance. Also, devices with a pseudowindow could have an increased coupling aperture, which results from the dielectric layers, and thus permits more light to enter the device. The light input facet of the device without a pseudowindow can be severely damaged during the cleavage process and AR coating, which may degrade the device dark current by several orders of magnitude. We also found that, even with partial recovery after rapid thermal annealing, devices without pseudowindows still suffer from damage and the maximum photocurrent is typically restricted to about 3 mA. The typical performance at -5 V of a device with a 100-/spl mu/m junction length and a 3-/spl mu/m pseudowindow is a responsivity of /spl sim/0.95 A/W responsivity and a /spl sim/5.5-GHz bandwidth at a wavelength of 1.3 /spl mu/m under 100-/spl mu/W illumination.

Post-weld-shift in semiconductor laser packaging

Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.

Effectiveness of metallic mirror for promoting the photoresponse of InGaAs PIN photodiode

Abstract The effectiveness of metallic mirror for raising the photoresponse of vertical-illuminated InGaAs PIN photodiode was calculated and experimentally verified. The preliminary results show that an InGaAs PIN photodiode with a 1-μm absorption layer and Ti/Pt/Au backside metallization can reach a responsivity of ∼0.8 A/W or a quantum efficiency of ∼76% at 1.3 μm wavelength. Such values indicate that the incident light travels the absorption region more than 1 μm and in turn provide the evidence for light reflection. From the comparison with the calculated responsivity spectra, the reflectivity of Ti/Pt/Au can be derived with a value of ∼0.4, which agrees reasonably well with the calculated metallic reflectivity.

Edge-coupled InGaAs P-I-N photodiode with a pseudowindow

We have experimentally verified that the incorporation of a pseudowindow with appropriate thickness can be advantageous for avoiding excessive surface leakage and improving quantum efficiency of edge-coupled InP/InGaAs/InP p-i-n photodiode (EC-PD). The window, which results in a passive facet, effectively protects the diode during facet cleavage and facet coating. Typical leakage density at -5 V of a facet-coated EC-PD with 2-/spl mu/m pseudowindow is lower than 1.5/spl times/10/sup -6/ A/cm/sup 2/ (30 pA). Also, due to the dielectric layers and the absence of alloyed metal/semiconductor interface on top of the window, the EC-PD could have an enlarged coupling aperture and reduced dissipative absorption. Nevertheless, for low-bias operation (e.g., /spl les/5 V), window thickness should be accurately controlled, otherwise excessive absorption in undepleted region would degrade the device performance. The optimal window thickness, which in fact is affected by experimental parameters (e.g., diffusion time), was determined to be about 2 to 3 /spl mu/m in this study according to the measurement results of efficiency and bandwidth.

Bandwidth enhancement for p-end-illuminated InP/InGaAs/InP p-i-n photodiodes by utilizing symmetrical doping profiles

This paper shows that the bandwidth of a p-end-illuminated planar InP-InGaAs-InP heterojunction p-i-n photodiode can be promoted by using a rather symmetrical doping profile that is produced through diffusion depth control. Caused by extra-depleted InP region in the end of p-InP, the device with symmetrical doping profile has additional series capacitance and thus has a smaller total capacitance than conventional asymmetrical doping profile. Such devices with 0.3 /spl mu/m depleted InP cap region, together with 1 /spl mu/m depleted InGaAs absorption region and 0.3 /spl mu/m depleted InP buffer region, having the capacitance as small as those devices with 1.6 /spl mu/m depletion region, while have the carrier transit time as short as those devices with 1.3 /spl mu/m depletion region. Under appropriate bias condition, which is required for getting rid of the heterointerface effects, the symmetrical device as stated with 40 /spl mu/m junction diameter can have a 3 dB bandwidth exceeding 17 GHz without inductance optimization. For device with conventional asymmetrical doping profile, that is, the p-n junction locating at /spl sim/0.1 /spl mu/m deep in the InGaAs layer, only a bandwidth of about 15 GHz can be obtained. Due to the same thickness of InGaAs absorption layer, both devices have similar responsivity of /spl sim/0.8 A/W at -5 V at 1.3 /spl mu/m wavelength. However, the heterointerface exposed in the depletion region results in several detrimental effects in symmetrical devices, such as interface-generation current, which leads to slightly increased dark current, and barrier/traps for hole transport, which lead to inferior photoresponse at low biases.

Thermally induced shifts in an optical fiber soldered into a ferrule

The thermally induced fiber shifts under a temperature cycling test of an optical fiber soldered into a ferrule packaging was measured experimentally. Up to a 0.18 /spl mu/m of the fiber shift was found in temperature cycling from -40 to +85/spl deg/C. This fiber displacement may arise from both the relief of the residual stresses and the intermetallic compound growth within the solder during the temperature cycling test. A finite-element method (FEM) analysis was also performed on the calculation of the up-bound fiber shift. Results showed that up to a 0.27 /spl mu/m of the fiber shift was predicted. This indicates that the FEM is an effective method for predicting the up-bound fiber shifts in temperature cycling test for laser module reliability study.

Effect of Au thickness on laser beam penetration in Invar-to-Invar packages

Comprehensive measurements of the dependence of the laser beam penetration on the Au coating thickness in laser welding techniques for semiconductor laser packages are presented. The results obtained from the Invar-Invar joints Show that the welded joints with thick Au coating exhibit narrower weld width, shallower penetration, and hence less joint strength than those the package joints with thin Au coating. A finite-element-method (FEM) is done of the effect of laser beam penetration On the Au thickness in the Invar-Invar joints. This method has been employed successfully to predict the laser beam penetration in laser welded Au-coated materials that the weld width and the penetration depth are found to be reduced as the Au coating thickness increases. The likely cause for the reduction is due to the increased thermal conduction of thicker Au in the welded region. Detailed knowledge of the effect of Au coating thickness on laser beam penetration is important for practical design and fabrication of reliable optoelectronic packaging having laser welded Au-coated materials.

Fiber alignment shift in temperature cycling test

A finite-element method (FEM) analysis has been carried out on the fiber alignment shift in an optical fiber soldered into a ferule. Results show that the maximum fiber alignment shifts are strongly depend on the geometry of fiber offset from the center of the ferrule.Up to 0.24 and 0.27 micrometers of the maximum fiber alignment shifts were predicted in temperature cycling from -40 to +85 degrees C and -40 to +100 degrees C, respectively. Detailed knowledge of predicting the maximum fiber alignment shift in temperature cycling test is important for practical design and fabrication of high yield optoelectronic packaging.

Recent developments in photonic devices for telecommunication applications in Taiwan

We report recent activities and achievements on the development of photonic devices for telecommunication applications. Opto-electronic devices such as high performance 1.55 μm complex-coupled InGaAsP-InP distributed feedback (DFB) and 1.3 μm uncooled AllnGaAs-InP lasers, the InGaAs-InP p-i-n photodetector on semi-insulating substrate, the 0.98 μm InGaAs-GaAs-InGaP pumping laser, and 12-channel laser and detector arrays, are presented. Work on the development of in-house vertical integration for the fabrication of a 1.55 μm single frequency transmitter, a 1.3 μm multimode transmitter and receiver, and an Er-doped fibre amplifier, and their applications in system trials in the Taiwan National Information Infrastructure network, is described.