Yuan-Kuang Tu

Long wavelength (1.3 μm) vertical-cavity surface-emitting lasers with a wafer-bonded mirror and an oxygen-implanted confinement region

We proposed and demonstrated a novel design for long wavelength (1.3 μm) vertical-cavity surface-emitting lasers (VCSELs). In this design, oxygen-implanted current-confinement regions were formed in a GaAs/AlGaAs Bragg reflector which is the bottom mirror wafer bonded to an AlGaInAs/InP cavity consisting of nine strain-compensated quantum wells. Room- temperature continuous-wave (cw) operation of 1.3 μm-VCSELs with a record low cw threshold current density of 1.57 kA/cm2 and a record low cw threshold current of 1 mA have been realized.

Thermal reliability and characterization of InGaP Schottky contact with Ti/Pt/Au metals

Abstract We present the characteristics of Ti/Pt/Au Schottky contacts on wide bandgap InGaP semiconductors with surface pre-treatment before Schottky contact deposition, and investigate the influence of post heat treatment on Schottky diodes. With the pre-deposition surface etching by dilute HCl, dilute NH 4 OH, or buffer oxide etchant (BOE), the performance of Schottky diodes compared with samples without surface pre-treatment is improved significantly. Auger electron spectroscopy (AES) analysis of the thermally annealed Schottky diode has been performed to investigate the failure mechanism. No significant change was found for samples annealed up to 450°C. However, a drastic degradation of the barrier height and the ideality factor was observed in samples annealed at 500°C, which may be caused by the interdiffusion and penetration of metals into the semiconductor.

InGaAs PIN photodiodes on semi-insulating InP substrates with bandwidth exceeding 14 GHz

Abstract The top-illuminated InGaAs PIN photodiodes have been fabricated from materials grown by metalorganic vapor phase epitaxy. Using the planar air-bridge approach and the selective etching technique, it can eliminate the significant bondpad capacitance which is present in conventional PIN photodiodes on conducting substrates. Besides, a self-aligned lift-off process is used for the n-contact recess and metallization. The anti-reflection coating devices have responsivity of 0.79 and 0.78 A/W at 1.3 and 1.55 μm, respectively. The fabricated devices with 30 μm photosensitive diameter have a very low dark current below 0.2 nA and low capacitance of 143 fF at −5V bias voltage. The 3-dB bandwidth of these devices is in excess of 14.8 GHz which is in good agreement with the calculated minority-carrier transit time through an absorbing layer thickness of 1.85 μm. The device performance reveals that these devices are potentially suitable for the applications in optoelectronic integrated circuits.

High performances and reliability of novel GaAs MSM photodetectors with InGaP buffer and capping layers

To avoid the trap-induced, low-frequency internal gain and improve the reliability for thermal storage test, a novel structure of GaAs metal-semiconductor-metal photodetector with InGaP buffer and capping layers is investigated. The dark current density of the photodetectors is about 7 /spl mu/A/cm/sup 2/. Its responsivity at 0.83-/spl mu/m wavelength is about 0.48 A/W. After thermal storage at 150/spl deg/C for 10 h, no performance degradation was found in the novel photodetectors.

Very-low-threshold, highly efficient, and low-chirp 1.55-μm complex-coupled DFB lasers with a current-blocking grating

Low-threshold current DFB lasers have been fabricated based on a complex-coupled structure with a current blocking grating. A threshold current as low as 5 mA was obtained, which enabled high temperature operation up to 105/spl deg/C. Asymmetric facet coatings were applied to obtain a high efficiency of 0.3 W/A. The strained InGaAsP MQW active region and the antiphase coupling has resulted in a low modulation chirping. By direct modulation of the device at 2.488 Gb/s and using optical amplifiers, we have demonstrated digital transmission over a 235 km-long standard single-mode fiber with a power penalty of 1.55 dB.

Low-chirp and high-power 1.55-/spl mu/m strained-quantum-well complex-coupled DFB laser

High-power, low-chirp, and low-threshold current characteristics of 1.55 /spl mu/m complex-coupled compressively strained InGaAsP quantum-well DFB laser with a loss grating are presented. Kink-free light-current characteristics with single-mode power over 40 mW are demonstrated for uncoated devices. A relatively low threshold current of 10 mA and a high slope efficiency of 0.23 W/A have been obtained even with the loss grating employed. Stable single-mode emission was demonstrated with a side mode suppression ratio up to 54 dB, a low chirp of less than 0.3 nm under 1 Gb/s pseudorandom digital modulation and a spectral linewidth of 8 MHz.

Low-threshold proton-implanted 1.3-μm vertical-cavity top-surface-emitting lasers with dielectric and wafer-bonded GaAs-AlAs Bragg mirrors

We demonstrate a new structure for long-wavelength (1.3-/spl mu/m) vertical-cavity top-surface-emitting lasers using proton implantation for current confinement. Wafer bonded GaAs-AlAs Bragg mirrors and dielectric mirrors are used for bottom and top mirrors, respectively. The gain medium of the lasers consists of nine strain-compensated AlGaInAs quantum wells. A record low room temperature pulsed threshold current density of 1.13 kA/cm/sup 2/ has been achieved for 15-/spl mu/m diameter devices with a threshold current of 2 mA. The side-mode-suppression-ratio is greater than 35 dB.

InGaPGaAs multiquantum barrier structures prepared by low-pressure organometallic vapor phase epitaxy

Abstract An InGaP GaAs superlattice with multiquantum barrier (MQB) effect was demonstrated by low-pressure organometallic vapor phase epitaxial technique. Two types of n-i-n tunnel diodes with either InGaP GaAs MQB barrier or bulk InGaP barrier were fabricated for comparison. The current-voltage characteristics show that the turn on voltage in the MQB barrier sample is higher than that in the bulk barrier sample. The experimentally measured effective barrier height of the MQB is about 1.8 times that of the bulk barrier, and this value is in quite good agreement with the value, 1.93, theoretically calculated by the transfer matrix method.

Low threshold 1.5 μm quantum well lasers with continuous linear‐graded‐index InGaAsP layers prepared by organometallic vapor‐phase epitaxy

We report quantum well heterostructures with continuous linear‐graded‐index quaternary (CL‐GRIN‐QW) prepared by low‐pressure organometallic vapor‐phase epitaxy for the first time, by adopting the empirical flow‐rate formulas. The linear compositional profile has been confirmed using secondary ion mass spectroscopy. Laser diodes incorporating the CL‐GRIN‐QW active layer structure exhibit threshold current density as low as 402 A/cm2 with a cavity length of 1500 μm and extrapolated threshold current density of infinite cavity length of about 176 A/cm2. These results demonstrate the benefits of the continuous linear‐graded‐index separate confinement layers for low threshold laser operation. Besides, the photoluminescence intensity of a continuous linear‐graded‐index strained‐quantum well structure is found to be higher than that of an equivalent unstrained well design.

High responsivity GaInAs PIN photodiode by using erbium gettering

In this article, we grow the GaInAs layers by introducing the rare-earth element Er into the GaInAs solutions for liquid-phase epitaxy without any complicated processes or an extended bakeout of the growth melts. The dominant process occurring during the growth of GaInAs layers in the presence of Er is a very efficient gettering of residual donors. By using an Er-doped GaInAs layer as the intrinsic layer in the PIN structure, the room temperature front-illuminated PIN photodiodes exhibit good quantum efficiencies of 60% at 1.3 /spl mu/m and 83% at 1.6 /spl mu/m for devices with antireflection coatings, which are better than those of 52% at 1.3 /spl mu/m and 65% at 1.6 /spl mu/m for the front-illuminated devices without Er doping and comparable to those of 63% at 1.3 /spl mu/m and 74% at 1.6 /spl mu/m for commercially available back-illuminated photodiodes. These devices also have a rise time of 88 ps and a pulsewidth of 162 ps for response speed and useful sensitivity to about 3.6 GHz. The detectors respond to pseudo-random modulation at bit rates up to 2.5 Gb/s with a clear eye opening and error free. >