GaAs-based Photodetectors Research Articles

Enhancing Photoresponse of GaAs-Based Photodetector by Plasmon Grating Structures

Nanostructured metal–semiconductor-metal photodetectors (MSM-PDs) can assist in future high-speed communication devices for achieving high responsivity characteristics. However, such devices suffer from low responsivity due to low absorption, and the large band gap limits its detection range. Herein, we propose a GaAs-based photodetector with enhanced photoresponse by plasmonic Au-GaAs grating structure. The design of a grating structure on the surface of n-GaAs can excite a plasmon mode to enhance the photoelectric performance of photodetectors. Consequently, under 795 nm incident light irradiation, the grating hybrid detector exhibits a nearly 4.2-fold increase in photocurrent compared to the bare GaAs device. The enhanced absorption can be up to 99% and a specific responsivity of 240 mA/W is realized. These results can thus provide a potential scheme to fabricate high-performance GaAs detector for numerous applications.

Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits

An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.

Optoelectronic properties comparison of 10 and 20 multi quantum wells Ga0.952In0.048N0.016As0.984/GaAs p-i-n photodetector for 1.0 μm wavelength

This study proves the addition of quantum wells to the intrinsic regions of p-i-n GaInNAs/GaAs has improved the performance of optoelectronic devices. The optoelectronic properties that contribute to the device's dark current and photocurrent need to be well understood to develop photo-response at longer wavelengths. This study reports an optoelectronic properties comparison of different quantum well number for Ga0.952In0.048N0.016As0.984/GaAs-based dilute nitride multi-quantum wells (MQWs) p-i-n photodetector devices. From photoluminescence (PL) analysis, 20 MQWs shows a higher PL peak than 10 MQWs. The maximum quantum efficiency (QE) is found to be 80.3% for 20 MQWs and 46% for 10 MQWs, where 20 MQWs being the highest QE value ever reported for GaInNAs-based MQWs photodetector. Current versus voltage (I–V) measurement shows that 20 MQWs produces lower dark current than 10 MQWs. Besides, 20 QWs sample produces a higher current density (−12.43 μAcm−2) than 10 MQWs (−7.52 μAcm−2) under illumination. Impedance spectroscopy analysis shows that a lower dark current of 20 MQWs is due to a high intrinsic resistivity and low dielectric loss peak compared to 10 MQWs. SimWindows simulation shows good correlation with responsivity analysis and impedance analysis where at −5 V, 20 MQWs produces higher responsivity (0.65AW-1) due to wider depletion region (deduce from conduction band profile) and lower intrinsic capacitance and dielectric loss (deduces from impedance analysis) than 10 MQWs (0.37AW-1). At room temperature, the detectivity (D*) of the 20 MQWs photodetector (7.12 × 1010 cmHz0.5W−1) is higher than 10 MQWS photodetector (4.89 × 1010 cmHz0.5W−1). Finally, the 20 MQWs's (4.02 × 10−11 WHz−0.5) has produces lower noise-equivalent power (NEP) than 10 MQWs (5.85 × 10−11 WHz−0.5). This study has succesfully presenting an understanding of optoelectronic properties and simultaneously producing a sensitive photodetector with high quality, low-noise which is comparable with ∼1010 cmHz0.5W−1 of commercial III-V alloy based near-infrared GaAs-based photodetectors.

Analysis of the influence and mechanism of sulfur passivation on the dark current of a single GaAs nanowire photodetector

Nanowire photodetectors, which have the advantages of fast response and high photoelectric conversion efficiency, can be widely applied in various industries. However, the rich surface states result in large dark current and can hinder the development of high-performance nanowire photodetectors. In this paper, the influence and mechanism of sulfur surface passivation on the dark current of a single GaAs nanowire photodetector have been studied. The dark current is significantly reduced by about 30 times after surface passivation. We confirm that the origin of the reduction of dark current is the decrease in the surface state density. As a result, a single GaAs nanowire photodetector with low dark current of 7.18 × 10−2 pA and high detectivity of 9.04 × 1012 cmHz0.5W−1 has been achieved. A simple and convenient way to realize high-performance GaAs-based photodetectors has been proposed.

Fabrication of high-quality GaAs-based photodetector arrays on Si

We report on fabrication and characterization of high-quality 32 × 32 GaAs photodetector (PD) arrays on Si substrates fabricated by wafer bonding and epitaxial lift-off (ELO) techniques. Fabricated GaAs PD arrays showed good crystal quality on Si substrates with Raman spectra and X-ray diffraction measurement. Also, pitch scaling gave us faster ELO process time as well as high-density PD arrays. Furthermore, we investigated electrical and optical characteristics of fabricated GaAs pin PD arrays on Si substrates. Especially, the components of dark current characteristics were also evaluated, because it is very important to explore further pitch scaling.

Analysis of dark currents and deep level traps in InP- and GaAs-based In0.83Ga0.17As photodetectors

InP- and GaAs-based metamorphic In0.83Ga0.17As photodetectors were grown and investigated. Compared to InP-based photodetector, the dark current of GaAs-based photodetector at room temperature increased 2–3 times but still comparable, whereas at 77K the dark current increased 2–3 orders. The deep-level transient spectroscopy results reveal that a deep level trap state exists in the GaAs-based photodetector structure. The higher dark current in GaAs-based photodetector at low temperature was mainly ascribed to a deep level trap induced tunneling current. The deep trap centers can also induce non-radiative recombination with smaller thermal active energy in the GaAs-based photodetector structure.

Subpicosecond electron-hole recombination time and terahertz-bandwidth photoresponse in freestanding GaAs epitaxial mesoscopic structures

We present the ultrafast (THz-bandwidth) photoresponse from GaAs single-crystal mesoscopic structures, such as freestanding whiskers and platelets fabricated by the top-down technique, transferred onto a substrate of choice, and incorporated into a coplanar strip line. We recorded electrical transients as short as ∼600 fs from an individual whisker photodetector. Analysis of the frequency spectrum of the photoresponse electrical signal showed that, intrinsically, our device was characterized by an ∼150-fs carrier lifetime and an overall 320-fs response. The corresponding 3-dB frequency bandwidth was 1.3 THz—the highest bandwidth ever reported for a GaAs-based photodetector. Simultaneously, as high-quality, epitaxially grown crystals, our GaAs structures exhibited mobility values as high as ∼7300 cm2/V·s, extremely low dark currents, and ∼7% intrinsic detection efficiency, which, together with their experimentally measured photoresponse repetition time of ∼1 ps, makes them uniquely suitable for terahertz-frequency optoelectronic applications, ranging from ultrafast photon detectors and counters to THz-bandwidth optical-to-electrical transducers and photomixers.

InGaAsN Metal–Semiconductor–Metal Photodetectors with Transparent Indium Tin Oxide Schottky Contacts

GaAs-based photodetectors (PDs) draw much attention owing to several advantages, such as low fabrication cost and the mature process techniques. However, fabricating them is a difficult task for the lack of suitable absorption materials that can be coherently grown on the GaAs substrate. In this report, we provide another approach to fabricate GaAs-based PDs, in which the novel InGaAsN alloy is used as the absorption layer. Three structures of planar PDs were demonstrated using transparent indium tin oxide (ITO) contacts. The dark current of PDs were suppressed by applying the SiO2 Schottky-barrier enhancement layer, but the rough interface between the SiO2 and InGaAsN layer limited the device characteristics. Depositing a thin layer of ITO between the SiO2 and InGaAsN layers greatly improved the interface quality and the photo current-to-dark current ratio was also increased from 17.7 to 45.29 under 0.5 V bias.

Mode coupling in a narrow spectral bandwidth quantum-dot microcavity photodetector

The resonant-cavity photodetector based on a quantum-dot (QD) absorbing region is analyzed and compared with experiment. We show that mode matching due to the low loss cavity in this type of photodetector is important in establishing the detection efficiency. In addition to extending GaAs-based photodetectors into the 1.3-μm wavelength regime, the QD active region can achieve an ultra-narrow spectral response because of its low absorption.

Evaluation of GaAs photodetectors for detection of soft X-ray pulses from laser-induced plasmas

GaAs-based photodetectors (lateral photoconductors and PIN photodiodes) are investigated with the aim to find good items to register nanosecond soft X-ray pulses generated from laser-induced plasmas. Pulse height spectra using light pulses that imitate X-ray pulses are measured and interpreted. Excitation with α particles were used to evaluate the loss of particle-induced charges in our detectors.

Optical photodetector for near-field optics

A p-n homojunction GaAs-based photodetector is developed in order to operate in the near field of a subwavelength sized light source. It has a spatial resolution of about 270 nm, limited by diffusion of minority carriers. A detector with a built-in AlGaAs diffusion barrier is also studied, demonstrating an improved resolution of better than 100 nm.