Pei-Chin Chiu

High-speed, high-responsivity, and high-power performance of near-ballistic uni-traveling-carrier photodiode at 1.55-/spl mu/m wavelength

In this letter, we demonstrate a novel photodiode at a 1.55-/spl mu/m wavelength: the near-ballistic uni-traveling-carrier photodiode (UTC-PD). After a p/sup +/ delta-doped layer was inserted into the collector of a UTC-PD, near-ballistic transport of photogenerated electrons under high reverse bias voltage (-5 V) and a high output photocurrent (/spl sim/30 mA) was observed. The demonstrated device has been combined with an evanescently coupled optical waveguide to attain high responsivity and high saturation power performance. Extremely high responsivity (1.14 A/W), a high electrical bandwidth (around 40 GHz), and a high saturation current-bandwidth product (over 1280 mA/spl middot/GHz, at 40 GHz) with high saturation radio-frequency power (over 12 dBm at 40 GHz) have been achieved simultaneously at a 1.55-/spl mu/m wavelength.

Analytical modeling of a high-performance near-ballistic uni-traveling-carrier photodiode at a 1.55-/spl mu/m wavelength

In this letter, we developed an analytical equivalent circuit model, which includes the resistance-capacitance-delay time and carrier transport time, to investigate the distinct dynamic performance of the near-ballistic uni-traveling-carrier photodiode (NBUTC-PD). This device, in which the structure of the collector of the UTC-PD is modified, can achieve excellent performance at a 1.55-/spl mu/m wavelength. According to the measured frequency responses of the scattering (S) parameters of NBUTC-PD and detailed device-modeling, the observed significant reduction of the device capacitance and the enhancement of the net optical-to-electrical bandwidth under high-power operation can be attributed to the unique near-ballistic-transport property of the photogenerated electron, which has never been observed in the traditional high-speed high-power photodiode.

Carrier dynamics of type-II InAs∕GaAs quantum dots covered by a thin GaAs1−xSbx layer

Carrier dynamics of InAs∕GaAs quantum dots (QDs) covered by a thin GaAs1−xSbx layer were investigated by time-resolved photoluminescence (PL). Both the power dependence of PL peak shift and the long decay time constants confirm the type-II band alignment at the GaAsSb–InAs interface. Different recombination paths have been clarified by temperature dependent measurements. At lower temperatures, the long-range recombination between the QD electrons and the holes trapped by localized states in the GaAsSb layer is important, resulting in a non-single-exponential decay. At higher temperatures, optical transitions are dominated by the short-range recombination with the holes confined to the band-bending region surrounding the QDs.

Effects of thermal annealing on the emission properties of type-II InAs/GaAsSb quantum dots

We report the effects of thermal annealing on the emission properties of type-II InAs quantum dots (QDs) covered by a thin GaAs1−xSbx layer. Apart from large blueshifts and a pronounced narrowing of the QD emission peak, the annealing induced alloy intermixing also leads to enhanced radiative recombination rates and reduced localized states in the GaAsSb layer. Evidences of the evolution from type-II to type-I band alignments are obtained from time-resolved and power-dependent photoluminescence measurements. We demonstrate that postgrowth thermal annealing can be used to tailor the band alignment, the wave function overlaps, and hence the recombination dynamics in the InAs/GaAsSb type-II QDs.

Effects of GaAsSb capping layer thickness on the optical properties of InAs quantum dots

The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime are found to be correlated with the capping layer thicknesses. Theoretical calculations indicate that the quantum confinement and the wave function distribution of hole states are sensitive to the GaAsSb capping layer thickness. The Sb induced change in QD size also plays a role in the optical properties of GaAsSb-capped QDs. Controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications. V C 2011 American Institute of Physics.

1.55μm emission from InAs quantum dots grown on GaAs

We report a comparative study on the growth of InAs quantum dots (QDs) on GaAs by metalorganic chemical vapor deposition using triethylgallium (TEGa) and trimethylgallium (TMGa) for the GaAs cap layer. QDs exhibit 1.3μm photoluminescence (PL) at room temperature, as the GaAs cap layer is directly grown on the QDs. The PL emission can be extended to 1.49μm when an In0.25Ga0.75As overgrown layer is inserted between the cap layer and the InAs QDs. The use of TMGa or TEGa for the growth of the GaAs cap layer is essential for a further increase in the emission wavelength of the InAs QDs. Strong PL emission at 1.55μm with a linewidth of 28meV can be obtained as the GaAs cap layer is grown by TEGa, while the optical properties degrade severely when using TMGa.

Enhancing the optical properties of InAs quantum dots by an InAlAsSb overgrown layer

The optical properties of InAs quantum dots (QDs) with a GaAs, an InAlAs, or an InAlAsSb overgrown layer are studied. For the InAs QDs with an InAlAsSb overgrown layer, their room temperature photoluminescence intensity is enhanced by as much as 4.5-fold compared to that of the QDs with an InAlAs one while maintaining similar narrow linewidth (26meV) and large ground-to first excited-state separation (103meV). The increase in radiative efficiency of the InAs∕InAlAsSb heterostructure is attributed to its better material quality due to the surfactant nature of Sb adatoms.

High-Performance Dual-Step Evanescently Coupled Uni-Traveling-Carrier Photodiodes

In this paper, we discuss a dual-step evanescently coupled photodiode (PD), which is composed of an improved evanescently coupled optical waveguide and a uni-traveling-carrier PD (UTC-PD). The hitherto serious dependence of the responsivity on the coupling length, which is determined by the cleaving process, or the necessity of a long (~ 700 mum) passive waveguide with a complex tapered structure, can be eliminated. The optimization of the waveguide structure, and the doping profile of the p-type absorption layer, allow the integrated UTC-PD to achieve a high responsivity (0.9 A/W, 1.04 A/W), with a large cleaving tolerance (~ 50 mum), a wide invariable electrical 3-dB bandwidth (60 GHz, 40 GHz) from a low (~ 0.5 mA) to a high output current (>13 mA), and a high saturation current-bandwidth product (around 780 mAGHz) simultaneously under a load of 50 Omega .

Device Characteristics of InGaSb/AlSb High-Hole-Mobility FETs

This letter reports the effect of growth temperature on carrier transport characteristics in In_0.4Ga_0.6Sb/AlSb heterostructure and demonstrates that hole mobility was enhanced by eliminating a parallel conducting channel in the buffer layers. Based on optimized growth conditions, hole mobility as high as 1220 cm²/V·s with carrier concentration of 1.3 ×10¹² cm^-2 was achieved. A 0.2- μm-gate-length In_0.4Ga_0.6Sb/AlSb p-channel device exhibited a maximum drain current of 102 mA/mm, a peak transconductance of 92 mS/mm, and an on-state breakdown voltage over 3 V. The pinchoff was observed for a gate bias of 0.6 V at drain current of 1 mA/mm. The current-gain and power-gain cutoff frequencies were 15 and 20 GHz, respectively.

Enhanced Normal-Incident Absorption of Quantum-Dot Infrared Photodetectors With Smaller Quantum Dots

Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.