Yulian Cao

Long Wavelength Infrared InAs/GaSb Superlattice Photodetectors With InSb-Like and Mixed Interfaces

We report on long wavelength infrared photodetectors using InAs/GaSb superlattices (SLs) with InSb-like and mixed interfaces (IFs). X-ray diffraction (XRD) measurements indicate that the SLs with mixed IFs have a narrower linewidth. The full-width at half-maximum of the XRD satellite peak is 24 arcsec for the sample with InSb-like IFs and is only 17 arcsec for the sample with mixed IFs. However, in terms of infrared photodetection, InSb-like IFs are superior to the mixed ones. Stronger photoluminescence and photoresponse signals are observed for the sample with InSb-like IFs.

High Structural Quality of Type II InAs/GaSb Superlattices for Very Long Wavelength Infrared Detection by Interface Control

We investigate the interface control for very long wavelength infrared InAs/GaSb superlattice (SL) structures. An InAs/GaSb SL photodetector with very high structural quality has been demonstrated by precisely controlling the Sb-soak, the growth stop time and the InSb layer thickness at the interfaces. The full width at half maximum of the X-ray diffraction satellite peaks of a p-i-n device structure is only 21 arcsec. The 50% cutoff wavelength of the detector is 14.5 μm at 77 K. At 14.5 μm, the quantum efficiency is 14%, while at the photoresponse maximum position of 7.7 μm it is 50%.

Mid Wavelength Type II InAs/GaSb Superlattice Photodetector Using SiOxNy Passivation

We report on a mid wavelength (MW) type II InAs/GaSb superlattice (SL) photodetector structure using SiOxNy as the passivation material. The 50% cutoff wavelength of the photoresponse is 4.8 µm at 77 K. R0A, the resistance-and-area product at zero bias, is 2.1×103 Ωcm2 for the device with the SiOxNy passivation, which is about 13 times larger than that without the passivation. Our result indicates SiOxNy passivation is an effective way to reduce the shunt current for MW InAs/GaSb SL photodetector.

Hybrid III–V/silicon laser with laterally coupled Bragg grating

In this paper, we demonstrate a compact electrically pumped distributed-feedback hybrid III-V/silicon laser with laterally coupled Bragg grating for the first time to the best of our knowledge. The hybrid laser structure consists of AlGaInAs/InP multi-quantum-well gain layers on top of a laterally corrugated silicon waveguide patterned on a silicon on insulator (SOI) substrate. A pair of surface couplers is integrated at the two ends of the silicon waveguide for the optical coupling and characterization of the ouput light. Single wavelength emission of ~1.55µm with a side-mode-suppression- ratio larger than 20dB and low threshold current density of 1.54kA/cm(2) were achieved for the device under pulsed operation at 20 °C.

High-Throughput Multiple Dies-to-Wafer Bonding Technology and III/V-on-Si Hybrid Lasers for Heterogeneous Integration of Optoelectronic Integrated Circuits

Integrated optical light source on silicon is one of the key building blocks for optical interconnect technology. Great research efforts have been devoting worldwide to explore various approaches to integrate optical light source onto the silicon substrate. The achievements so far include the successful demonstration of III/V-on-Si hybrid lasers through III/V-gain material to silicon wafer bonding technology. However, for potential large-scale integration, leveraging on mature silicon complementary metal oxide semiconductor (CMOS) fabrication technology and infrastructure, more effective bonding scheme with high bonding yield is in great demand considering manufacturing needs. In this paper, we propose and demonstrate a high-throughput multiple dies-to-wafer (D2W) bonding technology which is then applied for the demonstration of hybrid silicon lasers. By temporarily bonding III/V dies to a handle silicon wafer for simultaneous batch processing, it is expected to bond unlimited III/V dies to silicon device wafer with high yield. As proof-of-concept, more than 100 III/V dies bonding to 200 mm silicon wafer is demonstrated. The high performance of the bonding interface is examined with various characterization techniques. Repeatable demonstrations of 16-III/V-die bonding to pre-patterned 200 mm silicon wafers have been performed for various hybrid silicon lasers, in which device library including Fabry-Perot (FP) laser, lateral-coupled distributed feedback (LC-DFB) laser with side wall grating, and mode-locked laser (MLL). From these results, the presented multiple D2W bonding technology can be a key enabler towards the large-scale heterogeneous integration of optoelectronic integrated circuits (H-OEIC).

Self-Heating Effect on the Two-State Lasing Behaviors in 1.3-mu m InAs-GaAs Quantum-Dot Lasers

Experimental and theoretical study of the self-heating effect on the two-state lasing behaviors in 1.3-mu m self-assembled InAs-GaAs quantum dot (QD) lasers is presented. Lasing spectra under different injected currents, light-current (L-I) curves measured in continuous and pulsed regimes as well as a rate-equation model considering the current heating have been employed to analyze the ground-state (GS) and excited-state (ES) lasing processes. We show that the self-heating causes the quenching of the GS lasing and the ES lasing by the increased carrier escape rate and the reduced maximum modal gain of GS and ES.

Narrow-band long-/very-long wavelength two-color type-II InAs/GaSb superlattice photodetector by changing the bias polarity

We report on a narrow-band two-color photodetector using type-II InAs/GaSb superlattices (SLs) in the long-/very-long wavelength infrared (VLWIR) ranges by changing the polarity of the bias. The narrow-band photoresponse is achieved by sequentially growing the doped SL structure that has a shorter cutoff wavelength as a low-pass filter for the absorption layers that has a longer cutoff wavelength. At 77 K, the 50% cutoff wavelength of the photodiode is 10 μm when the applied bias voltage is –0.1 V and is 16 μm at +40 mV. The δλ/λ is 44% for the LWIR band and is 46% for the VLWIR band.

Three-region characteristic temperature in p-doped quantum dot lasers

We have investigated the temperature dependence of threshold in p-doped 1.3 μm InAs/GaAs quantum dot (QD) lasers with ten layers of QDs in the active region. It is found that the dependence of threshold current density on the temperature within the temperature range from 10 to 90 °C can be divided into three regions by its characteristic temperature (T0): negative, infinite, and positive T0 regions. Furthermore, the T0 region width is dependent on the cavity length: the longer cavity length of the QD lasers correspondingly the wider T0 region. Additionally, for the broad area laser, the threshold modal gains of the lasers with different cavity lengths can be fitted by an empirical expression as a function of the threshold current density, when at the temperatures of 30, 50, and 70 °C. We find that the transparency current density (Jtr) remains almost unchanged under different temperatures according to the extracted parameters from these fitted results, which indicates that Jtr plays an important role in b...

540-meV Hole Activation Energy for GaSb/GaAs Quantum Dot Memory Structure Using AlGaAs Barrier

We report on a memory structure that only makes use of holes as the storage charges based on type-II GaSb/GaAs quantum dots (QDs) using an AlGaAs barrier. The C-V measurements confirm existence of quantum states in the GaSb dots and reveal the applied bias voltage range for the write/erase process by charging/discharging the QDs. A large hole activation energy value of 540 meV is obtained for the device measured by deep level transient spectroscopy. Our results indicate that type-II GaSb/GaAs QD system is a promising candidate for future memory devices.

Passively mode-locked III-V/silicon laser with continuous-wave optical injection.

We demonstrate electrically pumped two-section mode locked quantum well lasers emitting at the L-band of telecommunication wavelength on silicon utilizing die to wafer bonding techniques. The mode locked lasers generate pulses at a repetition frequency of 30 GHz with signal to noise ratio above 30 dB and 1 mW average output power per facet. Optical injection-locking scheme was used to improve the noise properties of the pulse trains of passively mode-locked laser. The phases of the mode-locked frequency comb are shown to be coherent with that of the master continuous-wave (CW) laser. The radio-frequency (RF)-line-width is reduced from 7.6 MHz to 150 kHz under CW optical injection. The corresponding pulse-to-pulse jitter and integrated RMS jitter are 29.7 fs/cycle and 1.0 ps, respectively. The experimental results demonstrate that optical injection can reduce the noise properties of the passively mode locked III-V/Si laser in terms of frequency linewidth and timing jitter, which makes the devices attractive for photonic analog-to-digital converters and clock generation and recovery.