On-chip light detection using integrated microdisk laser and photodetector bonded onto Si board

Characteristics of a compact III–V optocoupler heterogeneously integrated on a silicon substrate and formed by a 31 µm in diameter microdisk (MD) laser with a closely-spaced 50 µm × 200 µm waveguide photodetector are presented. Both optoelectronic devices were fabricated from the epitaxial heterostroctructures with InGaAs/GaAs quantum well-dot layers. The measured dark current density of the photodetector was as low as 2.1 µA cm−2. The maximum link efficiency determined as the ratio of the photodiode photocurrent increment to the increment of the microlaser bias current was 1%–1.4%. The developed heterogeneous integration of III–V devices to silicon boards by Au-Au thermocompression bonding is useful for avoiding the difficulties associated with III–V epitaxial growth on Si and facilitates integration of several devices with different active layers and waveguides. The application of MD lasers with their lateral light output is promising for simplifying requirements for optical loss at III–V/Si interface.

A Schottky-Type Metal-Semiconductor-Metal Al0.24Ga0.76N UV Sensor Prepared by Using Selective Annealing

Asymmetric metal-semiconductor-metal (MSM) aluminum gallium nitride (AlGaN) UV sensors with 24% Al were fabricated using a selective annealing technique that dramatically reduced the dark current density and improved the ohmic behavior and performance compared to a non-annealed sensor. Its dark current density at a bias of −2.0 V and UV-to-visible rejection ratio (UVRR) at a bias of −7.0 V were 8.5 × 10−10 A/cm2 and 672, respectively, which are significant improvements over a non-annealed sensor with a dark current density of 1.3 × 10−7 A/cm2 and UVRR of 84, respectively. The results of a transmission electron microscopy analysis demonstrate that the annealing process caused interdiffusion between the metal layers; the contact behavior between Ti/Al/Ni/Au and AlGaN changed from rectifying to ohmic behavior. The findings from an X-ray photoelectron spectroscopy analysis revealed that the O 1s binding energy peak intensity associated with Ga oxide, which causes current leakage from the AlGaN surface, decreased from around 846 to 598 counts/s after selective annealing.

Influence of Pixel Etching on Electrical and Electro-Optical Performances of a Ga-Free InAs/InAsSb T2SL Barrier Photodetector for Mid-Wave Infrared Imaging

In this paper, the influence of etching depth on the dark current and photo-response of a mid-wave infrared Ga-free T2SL XBn pixel detector is investigated. Two wet chemical etching depths have been considered for the fabrication of a non-passivated individual pixel detector having a cut-off wavelength of 5 µm at 150 K. This study shows the strong influence of the lateral diffusion length of a shallow-etched pixel on the electro-optical properties of the device. The lowest dark current density was recorded for the deep-etched detector, on the order of 1 × 10−5 A/cm2 at 150 K and a bias operation equal to −400 mV. The corresponding quantum efficiency was measured at 60% (without anti-reflection coating) for a 3 µm thick absorbing layer. A comparison of experimental results obtained on the two kinds of etched pixels demonstrates the need for a deep-etching process combined with efficient passivation for FPA manufacturing.

Simulation of AlGaN MSM detector for investigating the effect varying absorber layer thickness

For detecting feeble Ultra-Violet (UV) signals it is essential that front-illuminated photodetector (PD) should havethick photo-absorbing layer with thin transparent metal electrodes and antireflective coating (ARC) so as to getmore photocurrent and low dark current.Since detector geometry influences its performance, so it is very important to optimize layer thickness parameters. In proposed work fixed area Al0.5Ga0.5N/AlN/ Sapphire based Metal-Semiconductor-Metal (MSM)PDbased has been analyzed for optimum value of active layer thickness and inter-electrode thickness.In addition to take benefit of large Schottky barrierGold material has beenutilized for electrodes. It has been illustrated in past research studies that with the increase in thickness of AlGaN layer, more incident energy can be absorbed for large EHPs generation which lead to increased responsivity.However, few research papers have related the effect of variations inthickness of active layerwith electron velocity which has significant effect on dark current density, recombination rateand additionally on efficiency.So for further development and widespread implementation of AlGaN/GaN based detectors there is need to study the effect of variation in photo-absorber layer thickness on closely related performance parameters so as to select its optimum value.Current Voltage (IV)-characteristics,recombination rate, current density plots and spectral response have been investigated using Atlas-Silvaco simulation tool.In addition for electrode thickness variation,transmission and absorptionplots are alsoinvestigated. For the proposed MSM structure, it has been observed that dark current density tends to increase beyond the optimum value of thickness of AlGaN layerwith specific absorption coefficient. Good transmission of light with high spectral response can be obtained with optimum value of electrode thickness.These observations can be suitable for improving the detectivity in support of various UV detection applications requiring good sensitivity and high signal to noise ratio.

Improvement of Photoelectrochemical Properties of WO3 Photoelectrode Fabricated by Using H2O2 Additive

In this study, we deposited a WO3 thin-film photoelectrode on a fluorine-doped tin oxide (FTO) substrate using a spin-coating method, and we investigated the photocurrent density and dark current density of the WO3 photoelectrode with various amounts of H2O2 additive. The morphological, structural, optical, electrical and photoelectrochemical properties of the WO3 photoelectrode with various amounts of H2O2 additive were analyzed using FE-SEM, XRD, UV-vis spectroscopy, EIS and a three-electrode potentiostat/galvanostat system, respectively. The amount of H2O2 additive has a large influence on the thickness of the WO3 photoelectrode, XRD (100) peak intensity, light absorption, optical energy bandgap, flat-band potential, donor density value, etc., and thus has a large influence on photoelectrochemical properties. Specifically, the H2O2 additive had a large influence on the growth of the WO3 photoelectrode, and the photocurrent density and dark current density characteristics of the WO3 photoelectrode grown to a uniform and thick thickness were largely improved. As a result, the WO3 photoelectrode fabricated with 0.2 mL of added H2O2 exhibited a high photocurrent density value of 1.17 mA/cm², which was about 23 times higher than that of the WO3 photoelectrode fabricated without H2O2 additive, and had a dark current density value of a low 0.04 mA/cm², which was a reduction of about 87%.

Semiconductor Photodetectors

This chapter describes the operating principles of photoconductive and photovoltaic detectors based on III–V semiconductors. The electrical characteristics of both photodiodes and majority carrier barrier structures are discussed starting with the diffusion equation. The chapter outlines the figures of merit used to evaluate the performance of infrared photodetectors including the responsivity, dark current density, and normalized detectivity. It discusses bulk-like and type II superlattice photodetectors and how the multistage arrangement of interband cascade detectors (ICDs) can reduce the dark current density at the expense of a lower responsivity. Detectors that employ intersubband optical transitions, namely, quantum-well infrared photodetectors and quantum cascade detectors, are also discussed. The chapter considers how the dark-current density can be suppressed in resonant-cavity and thin waveguide-based detectors. It concludes with a discussion of the requirements for high-speed operation and an overview of novel types of detectors that draw their inspiration from III–V semiconductor devices.