Chih-Chao Yang

10-Gb/s InGaAs p-i-n Photodiodes With Wide Spectral Range and Enhanced Visible Spectral Response

By selectively removing the InP cap layer on top of the conventional double-heterojunction InP-InGaAs-InP p-i-n photodiodes (PDs), a PD with high quantum efficiency in the 0.55- to 1.65-mum spectral range was realized. With antireflection coating designed both for 0.85- and 1.3-mum wavelengths, quantum efficiency higher than 80% in the 0.85- to 1.65-mum range and higher than 70% in the 0.55- to 1.65-mum range was achieved. In addition, we use a novel chip-level package technique, a self-positioned micro-ball-lens on chip, to get a large spatial alignment tolerance for the PDs. The combination of these two features significantly enhances the spectral and spatial detection range of our 10-Gb/s InGaAs p-i-n PD. Besides, exhibiting a dark current smaller than 50 pA, the PD has a 3-dB bandwidth higher than 10.3 GHz at 1.3-mum wavelength. At the 10.3-Gb/s data rate, back-to-back eye diagrams of the PD are both wide open at 0.85- and 1.3-mum wavelengths. Since both high-efficiency and high-speed operation can be achieved, receivers based on such devices are suitable for both 0.85- and 1.3-mum single-mode and multimode fiber-optic communication systems

Formation and Microstructure of Mesoporous Silica Films with Ultralow Dielectric Constants

SiuCH3 and SiuOH groups in the mesoporous silica film. The surface roughness of the calcined films was characterized by atomic force microscopy ~AFM! and scanning electron microscopy ~SEM!. The thickness of calcined mesoporous silica film was measured by cross-sectional SEM. Thermal desorption mass spectrometry ~TDSMS! was used to study the thermal stability of trimethylsilyl groups and hydrophobicity of mesoporous silica film. Auger electron spectroscopy ~AES! was used to investigate the elementary composition of film samples. Dielectric properties and leakage current measurements were implemented through the fabrication of metal-insulatorsemiconductor ~MIS! capacitors. Prior to measurement, the back side of a coated wafer was treated with diluted hydrofluoric acid to remove native oxide, and then coated with aluminum to form a better back contact. An array of aluminum dots was fabricated on the top side of the silica film by thermal evaporation with a shadow mask. A Keithley model 82 CV meter was used to measure the high-frequency capacitance-voltage ~C-V! curves at 1 MHz, and dielectric constants of the films were calculated from the capacitance and thickness of the films. The leakage current density of silica films was determined from current-voltage ~I-V! characteristics performed on an HP 4156 semiconductor parameter analyzer.

Low-cost and high-performance 1.3-/spl mu/m AlGaInAs-InP uncooled laser diodes

In this letter, we utilize a self-terminated oxide polish (STOP) planarization technique to fabricate high-yield, high-performance, low-cost, and uncooled 1.3-mum ridge-waveguide AlGaInAs-InP laser diodes (LDs). The STOP technique is superior to the polyimide planarization, which suffers from high-temperature sustainability. The LDs fabricated by the STOP technique exhibit threshold currents of 8.5 and 30.5 mA, and light output powers of 25.9 and 4.8 mW at 100 mA for 20degC and 110degC, respectively. The characteristic temperatures (T 0) are 82.6 K from -30degC to 80degC and 55.9 K from 80degC to 110degC. Since the metal pad lies on a thick SiO2 layer, the parasitic capacitance can be effectively lowered to 2 pF. The 3-dB modulation bandwidths of the LDs at 50 mA are 12.1 and 9.44 GHz at 20degC and 90degC, respectively

Alignment tolerance enlargement of a high-speed photodiode by a self-positioned microball lens

By integrating a commercially available microball lens on the InGaAs p-i-n photodiode chip, we have achieved at least 5- and 16-fold improvements of the optical alignment tolerance in the transverse and longitudinal axes, respectively, without sacrificing the diode efficiency. The optical alignment during lens/chip integration is achieved by a self-positioning process, which provides an on-chip ball-lens socket in concentric circles to the photodiode aperture to sustain the drop-in microball lens. The photodiode after lens integration exhibits a 3-dB bandwidth larger than 9 GHz and a responsivity larger than 0.9 A/W, both at 1310-nm wavelength. In addition, the InGaAs photodiode exhibits a dark current density of less than 3 /spl mu/A/cm/sup 2/, both before and after lens positioning, indicating a proper integration.

Self-terminated oxide polish technique for the waveguide ridge laser diode fabrication

Semiconductor lasers fabricated by the traditional process for communication application usually adopt a ridge-waveguide structure for its ease of manufacture. However, the rugged planes of these devices would cause metal coverage problems and interconnection difficulty. A planarization technique based on a self-aligned technique for fabricating the ridge-weaveguide semiconductor laser diode is introduced in this article. The technique is based on a process called “self-terminated oxide polish.” By using this technique, metal coverage problems usually encountered in the laser diode with a double trench structure will be reduced. Since the metal pad lies on a thick oxide layer, the device will also have a lower parasitic capacitance, which will be beneficial to high-speed operation. Device characteristics of several ridge-waveguide laser diodes fabricated using this self-aligned method will be presented.

Monte Carlo ray trace simulation for micro-ball-lens-integrated high-speed InGaAs p-i-n photodiodes

To widen the alignment tolerance of a 10Gbytes∕s InGaAs p-i-n photodiode, which typically only has an optical coupling aperture of 30μm in diameter, we have developed a self-positioning ball-lens-on-chip scheme for enlarging the effective coupling aperture. According to the measured results, the 4.5- and 5.3-fold improvements along the transverse and optical axes, respectively, in alignment tolerance have been demonstrated without sacrificing the diode efficiency as a commercially available ruby micro-ball-lens (MBL) with a 300μm lens diameter integrated on the high-speed photodiode. To further explore the aperture enlargement capability and optimize the structural design, we have constructed a ray trace model based on the Monte Carlo method for the optical coupling system as well. Using this well-constructed simulation model, we further predict that, by integrating a 250μm diametric ruby MBL on the photodiode with a 20μm high lens socket, the alignment tolerance can have 7.1- and 10-fold improvements alo...

A simple and low-cost fabrication of polymeric vertical microlens using dip method

Polymeric vertical microlenses (PVMs) using photoresist material SU-8 are fabricated with a simple and low-cost process that can be easily applied to the microoptical/optoelectronic bench. By virtue of the strong adhesive force and liquid cohesion, the PVMs are formed by hanging the liquid SU-8 on walls by a dip method. Then, in order to enhance the thermal stability and reliability of the PVMs, the lenses are baked and exposed in the ultraviolet light to crosslink the SU-8. To characterize the PVMs, we use a single-mode fiber carrying a 1.55-/spl mu/m wavelength laser light source and utilize BeamScope P5 to observe the beam convergences. The output beams through the PVMs show a vertical far-field angle of 3.04/spl deg/, as compared to 5.53/spl deg/ of the beam without passing through the lenses.

High-Temperature and High-Frequency Operation of 1.3 μm AlGaInAs ∕ InP Laser Diodes Using Silicon Oxide Planarization

In this article, a self-terminated oxide polish (STOP) planarization technique is utilized to fabricate high-temperature and highspeed 1.3 μm AlGaInAs/InP ridge-waveguide laser diodes (LDs). The as-cleaved LDs fabricated by this STOP technique exhibit a threshold current of 8.5 and 57.5 mA, and a light output power of 27 and 2.4 mW at 100 mA for 0 and 130°C, respectively. The characteristic temperature (To) is 85.5 K from 0 to 80°C and 54.1 K from 80 to 130°C. The full width at half maximum of the lateral far-field angle is 34° for the conventional ridge LDs and reduces to 22° for the LDs by the STOP technique. The 3 dB modulation bandwidth at 100 mA of the LDs can reach 16.9 at 20°C and 10.9 GHz at 90°C.

Fabrication of a polymeric vertical microlens with the dip method

We have investigated a process based on the dip method to fabricate a polymeric vertical microlens (PVM). After the primary dip step, the PVM is formed by hanging the liquid SU-8 on a wall in virtue of the strong adhesive force and liquid cohesion. The microlens is then baked and exposed in ultraviolet light to further cross-link the negative photoresist SU-8 to enhance thermal stability and reliability. According to the experimental results, the radius of curvature of the fabricated vertical microlens varies from 120.8 to 34.2 microm, which relates to the dip depth or the thickness of the dipped pool. To characterize the PVM, an edge-emitting laser diode (lambda=1.31 microm) is then bonded onto the optical bench and a detector is utilized to observe the beam divergence with and without the lens insertion. Compared with an angle of 40.8 degrees without the microlens, the beam passing through a suitable PVM shows a vertical far-field angle of 3.32 degrees. Furthermore, the lens efficiency, approximately 83.4%, is also specified by the measurements.