Metal-semiconductor-metal Photodetectors Research Articles

Enhancing photoresponse time of low cost Pd/ZnO nanorods prepared by thermal evaporation techniques for UV detection

High quality undoped ZnO nanorods have been synthesized at 850 °C by vapor–solid (VS) technique without a catalyst through a low cost process on silicon substrates. Then, ZnO nanorods have been characterized by using scanning electron microscopy (SEM), X-ray diffractometer (XRD), and photoluminescence (PL) spectroscopy. Metal–semiconductor–metal (MSM) photodetectors with palladium (Pd) as contact electrodes have been successfully constructed for ultraviolet (UV) detection. Under dark and UV illumination, the load resistance of the Pd/ZnO junction was found to be 80.4 kΩ, and 23.5 kΩ referring to the maximum allowed bias voltage; the barrier height was estimated to be about 0.8 eV, and 0.76 eV, at 5 V applied bias voltage, respectively. It was found that the maximum responsivity of the Pd/ZnO MSM photodetector was 0.106 A/W at 300 nm which corresponds to a quantum efficiency of 43.8% at 5 V applied bias voltage. The transient photoresponse of the fabricated device is reported under different applied biases at 1 V, 3 V, and 5 V.

Large-area solar-blind AlGaN-based MSM photodetectors with ultra-low dark current

Large-area metal–semiconductor–metal (MSM) solar-blind photodetectors with a device area of 5×5 mm2 have been fabricated on Al0.4Ga0.6N/AlN/sapphire epistructure. The photodetector exhibits ultra-low dark current density of 3.2×10−12 A/cm2 under 20 V bias and a corresponding breakdown voltage of up to 385 V. The solar-blind/ultraviolet rejection ratio of the photodetector is more than four orders of magnitude with a maximum quantum efficiency of 28% at 275 nm.

Performance optimization of a free space optical interconnect system with a metal-semiconductor-metal detector

In this paper we study the possibility and the potentiality of using metal semiconductor-metal photodetector (MSM-PD) in three-dimensional parallel free space optical interconnect (FSOI) systems. The signal-to-noise ratio (SNR) and time response are used as performance measures to optimize the geometry of MSM-PD used in FSOI systems. Both SNR and time response are evaluated, analyzed, and their dependence on feature parameters of the MSM-PD, including finger size, spacing, and number of fingers, are considered. Based on the results obtained, we show that the use of MSM-PD in FSOI improves the interconnect speed at a given acceptable SNR.

Metal-semiconductor-metal (MSM) photodetectors with plasmonic nanogratings*

We discuss the light absorption enhancement factor dependence on the design of nanogratings inscribed into metal-semiconductor-metal photodetector (MSM-PD) structures. These devices are optimized geometrically, leading to light absorption improvement through plasmon-assisted effects. Finite-difference time-domain (FDTD) simulation results show ~50 times light absorption enhancement for 850 nm light due to improved optical signal propagation through the nanogratings. Also, we show that the light absorption enhancement is strongly dependent on the nanograting shapes in MSM-PDs.

A 2 Gb/s optical receiver with monolithically integrated MSM photodetector in standard CMOS process

A monolithically standard complementary-metal-oxide-semiconductor (CMOS) optical receiver with a metal-semiconductor-metal (MSM) photodetector is presented in this paper. An active-feedback transimpedance amplifier (TIA) with negative Miller capacitance is used to increase the bandwidth of the receiver. The MSM photodetector with high responsivity provides higher sensitivity for the optical receiver. The optical receiver implemented in chartered 0.35 μm process achieves a 1.7 GHz bandwidth due to the low capacitance of the MSM photodetector. 2 Gb/s optical data are successfully transmitted with a bit-error rate of 10−9 at an optical power of −15 dBm. The power consumption of the receiver is 94 mW under a single 3.3 V supply.

Picosecond response times in GaAs/AlGaAs core/shell nanowire-based photodetectors

High-speed metal-semiconductor-metal (MSM) photodetectors based on Schottky-contacted core/shell GaAs/AlGaAs and bare GaAs nanowires were fabricated and characterized. The measured core/shell temporal response has a ∼10 ps full-width at half-maximum and an estimated corrected value less than 5 ps. The bare GaAs devices exhibit a slower response (∼35 ps) along with a slow decaying persistent photocurrent (∼80 s). The core/shell devices exhibit significantly improved dc and high-speed performance over bare nanowires and comparable performance to planar MSM photodetectors. The picosecond temporal response, coupled with picoampere dark current, demonstrate the potential for core/shell nanowires in high-speed imaging arrays and on-chip optical interconnects.

Ultraviolet photodetectors based on MgZnO thin films

In this work, Ti/Au Ohmic contacts to both Mg0.24Zn0.76O and ZnO film-based metal-semiconductor-metal (MSM) photodetectors (PDs) were fabricated on glass substrates for comparative analysis. The transmittance spectra measured around the optical energy gap revealed that Mg0.24Zn0.76O films have a larger optical energy gap (3.54 eV) than ZnO films (3.25 eV). Mg0.24Zn0.76O MSM-structured ultraviolet (UV) PDs show a much higher UV-to-visible rejection ratio of 2.78×103 than those made of ZnO films. This can be attributed to the low dark current (0.08 pA) of the Mg0.24Zn0.76O UV PDs and the small full width at half maximum (0.34°) of the Mg0.24Zn0.76O (002) x-ray diffraction peak, indicating better crystal quality than that of ZnO. With an applied bias of 5 V and illuminations at 350 and 380 nm, the Mg0.24Zn0.76O and ZnO film-based MSM PDs exhibited responsivities of 0.4 and 0.32 A/W, respectively.

GaN-Based Metal–Semiconductor–Metal Ultraviolet Photodetectors with the ZrO2 Insulating Layer

GaN metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors (PDs) with ZrO2 insulating layers were successfully fabricated and characterized. It was found that we can achieve a small dark current and large photocurrent to dark current contrast ratio from the proposed devices with the use of ZrO2 insulating layers. With a 20 V applied bias, it was found that the leakage current of the fabricated MSM PDs with ZrO2 insulating layers was 1.73 ×10-10 A. This small leakage current should be attributed to the large barrier height caused by the insertion of the ZrO2 insulating layers. We can also achieve a large UV to visible rejection ratio from the PDs with ZrO2 insulating layers. Furthermore, it was also found that we can significantly reduce noise equivalent power and enhance detectivity by using ZrO2 insulating layers.

GaN-Based Metal–Semiconductor–Metal Ultraviolet Photodetectors with the ZrO2Insulating Layer

GaN metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors (PDs) with ZrO2 insulating layers were successfully fabricated and characterized. It was found that we can achieve a small dark current and large photocurrent to dark current contrast ratio from the proposed devices with the use of ZrO2 insulating layers. With a 20 V applied bias, it was found that the leakage current of the fabricated MSM PDs with ZrO2 insulating layers was 1.73 ×10-10 A. This small leakage current should be attributed to the large barrier height caused by the insertion of the ZrO2 insulating layers. We can also achieve a large UV to visible rejection ratio from the PDs with ZrO2 insulating layers. Furthermore, it was also found that we can significantly reduce noise equivalent power and enhance detectivity by using ZrO2 insulating layers.

Dark current suppression in an erbium–germanium–erbium photodetector with an asymmetric electrode area

In this work, suppression of the dark current level in a metal-semiconductor-metal (MSM) photodetector fabricated on the intrinsic (i) Ge is achieved by exploiting (1) the Er electrode, providing a relatively high hole barrier, and (2) the concept of asymmetric electrode area, to minimize the Schottky barrier height lowering effect. Compared with a symmetric MSM photodetector fabricated with Ti electrodes, the dark current level was reduced by a factor of about 80. This low dark current i-Ge MSM photodetector is promising for applications requiring low power and a high photo-to-dark-current ratio.

Application of Nanoporous Silicon for a Metal-Semiconductor-Metal Visible Light Photodetector

In this paper we present a study on the application of nanoporous silicon to an optoelectronic device called a nanoporous silicon metal-semiconductor-metal (MSM) visible light photodetector. This device was fabricated on a nanoporous silicon layer which was formed by electrochemical etching of a silicon wafer in a hydrofluoric acid solution under various anodization conditions such as the resistivity of the silicon wafer, current density, concentration of the hydrofluoric acid solution and anodization time. The structure of this device has two square Al/nanoporous silicon Schottky-barrier junctions on the silicon substrate and the electrode spacing is 500 microm. The experiment will study photoresponse and the response time of a nanoporous silicon MSM photodetector which was fabricated on the various porosity of a nanoporous silicon layer. It is found that when devices are fabricated on a higher porosity nanoporous silicon layer, the photoresponse of the device will expand toward the short-wavelength and the bandwidth of the spectrum response will cover visible light. In addition, it is found that the response time of the device decreases.

ZnO金属半导体金属光电探测器特性的理论优化

A two-dimensional model of a metal-semiconductor-metal (MSM) ZnO-based photodetector (PD) is developed. The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential distribution inside the structure, the transversal and longitudinal distributions of the electric field, and the distribution of carrier concentration. The ohmicity of the contact has been confirmed. The dark current of MSM PD based ZnO for different structural dimensions are likewise calculated. The calculations are comparable with the experimental results. Therefore, the influence with respect to parameters s (finger spacing) and w (finger width) is studied, which results in the optimization of these parameters. The best optimization found to concur with the experimental results is s = 16 \mu m, w = 16 \mu m, l = 250 \mu m, L = 350 \mu m, where l is the finger length and L is the length of the structure. This optimization provides a simulated dark current equal to 24.5 nA at the polarization of 3 V.

Analysis of nano-grating-assisted light absorption enhancement in metal–semiconductor–metal photodetectors patterned using focused ion-beam lithography

We present finite-difference time-domain (FDTD) analysis results of light absorption enhancement factor dependence on the profile shape of nano-gratings etched into the surfaces of metal–semiconductor–metal photodetector (MSM-PD) structures. The MSM-PDs patterned by nano-gratings are optimized geometrically, improving the light absorption near the design wavelength through plasmon-assisted electric field concentration effects. FDTD simulation results show about 50 times light absorption enhancement prediction for 850 nm light due to improved optical signal propagation through the nano-gratings in comparison with the conventional MSM-PD designs employing only a subwavelength aperture. We also report on the nano-grating profile shapes obtained typically in our experiments using focused ion-beam lithography and discuss the dependency of light absorption enhancement on the geometric parameters of nano-gratings inscribed into MSM-PDs.

NANOPOROUS SILICON METAL-SEMICONDUCTOR-METAL PHOTODETECTOR

In this paper we present a study on the application of nanoporous silicon to an optoelectronic device called a nanoporous silicon metal-semiconductor-metal (MSM) visible light photodetector. This device was fabricated on a nanoporous silicon layer which was formed by electrochemical etching of a silicon wafer in a hydrofluoric acid solution under various anodization conditions such as the resistivity of the silicon wafer, current density, concentration of the hydrofluoric acid solution and anodization time. The structure of this device has two square Al /nanoporous silicon Schottky-barrier junctions on the silicon substrate and the electrode spacing is 500 μm. The experiment will study photoresponse and the response time of a nanoporous silicon MSM photodetector which was fabricated on the various porosity of a nanoporous silicon layer. It is found that when devices are fabricated on a higher porosity nanoporous silicon layer, the photoresponse of the device will expand toward the short-wavelength and the bandwidth of the spectrum response will cover visible light. In addition, it is found that the response time of the device in terms of rise time will decrease.

Effects of High-Energy Electron Irradiation on ZnO/Si MSM Photodetectors

ZnO/Si metal–semiconductor–metal photodetectors (MSM-PDs) were subjected to high-energy electron irradiation (HEEI) to total fluence of 2 × 1013 cm−2. ZnO/Si MSM-PDs demonstrated at least 43% greater radiation resistance than similar Si devices. Room-temperature annealing of radiation damage was observed as 63% recovery of photocurrent over 47 days. The current transport mechanism for ZnO/Si MSM-PDs was dominated by space-charge-limited conduction (SCLC) with minimal effect on conduction regime due to HEEI. Analysis of photoluminescence (PL) data indicates that the radiation-induced defects are likely oxygen and zinc vacancies, i.e., (V 0 + ) and $$ (\hbox{V}_{\rm{Zn}}^{ - } - \hbox{H}^{ + } )^{0} $$ , respectively.

ZnO-based interdigitated MSM and MISIM ultraviolet photodetectors

The paper reports the fabrication and characterization of ZnO-based interdigitated metal–semiconductor–metal (MSM) and metal–insulator–semiconductor–insulator–metal (MISIM) ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si ⟨1 0 0⟩ substrate by the sol–gel technique. With applied voltage in the range from −3 to 3 V we estimated the contrast ratio, responsivity, detectivity and quantum efficiency of the photodetectors for an incident optical power of 0.1 mW at 365 nm ultraviolet wavelength. The I–V characteristics were studied and the parameters such as ideality factor, leakage current and barrier height were extracted from the measured data. For Au/Cr/SiO2/ZnO/SiO2/Al (MISIM) structure the product (mχ) of the tunnelling effective electron mass (m) and the mean tunnelling barrier height (χ) was also extracted.

Thermally stable Ir/n-ZnO Schottky diodes

Temperature-dependent characteristics of ZnO Schottky diodes with Iridium (Ir) contact electrodes were investigated. Using Norde model, it was found that the effectively Schottky barrier heights of Ir on n-ZnO were around 0.837, 0.829, 0.801, 0.750 and 0.719 eV when measured at 25, 30, 50, 100 and 150 °C, respectively. Using Cheung’s method, it was found that Schottky barrier heights between Ir and the n-ZnO were 0.824, 0.823, 0.789, 0.743 and 0.740 eV when measured at 25, 30, 50, 100 and 150 °C, respectively. The large Schottky barrier heights suggest that Ir is a potentially useful material for ZnO-based ultraviolet Schottky barrier photodetectors and metal–semiconductor-metal photodetectors.

Study of Ge embedded inside porous silicon for potential MSM photodetector

Purpose – The purpose of this paper is to describe a very low‐cost way to prepare Ge nano/microstructures by means of filling the material inside porous silicon (PS) using a conventional and cost effective technique in which thermal evaporator with PS acts as patterned substrate. Also, the potential metal‐semiconductor‐metal (MSM) photodetector IV characteristics of the structure are demonstrated.Design/methodology/approach – PS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid. The Ge layer was then deposited onto the PS by thermal evaporation. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10 min. Structural analysis of the samples was performed using energy dispersive X‐ray analysis (EDX), scanning electron microscope (SEM), X‐ray diffraction (XRD) and Raman spectroscopy.Findings – A uniform circular network distribution of pores is observed with sizes estimation of 100 nm to 2.5 μm by SEM. Also observed are cluster...

Fast Lateral Amorphous-Selenium Metal–Semiconductor–Metal Photodetector With High Blue-to-Ultraviolet Responsivity

A lateral metal-semiconductor-metal (MSM) photodetector with a layer of thin amorphous selenium (a-Se) is investigated to detect visible photons. A comparative study on detectors with different a-Se thicknesses is conducted. The thinner detector tends to have better optoelectronic performance, having a low dark current in the range of 40-180 fA under various lateral biases over 1000 s, high responsivity up to ~0.45 A/W toward a short wavelength of 468 nm, and high speed of photoresponse up to 2 kHz with signal rise time of 50 μs and fall time of 60 μs. The fast lateral a-Se MSM photodetector thus has enormous potential to be used in a variety of optical sensing applications, particularly in large-area digital indirect-conversion X-ray imaging.

Characterization of Mg0.20Zn0.80O metal–semiconductor–metal photodetectors

Abstract Mg 0.20 Zn 0.80 O films have been prepared on quartz substrates by using radio frequency (RF) magnetron sputtering, and metal–semiconductor–metal (MSM) structured photodetectors have been fabricated on the Mg 0.20 Zn 0.80 O films employing interdigital Au as metal contacts. We have investigated the effects of electrode spacings on the properties of Mg 0.20 Zn 0.80 O MSM photodetectors. It was shown that both of dark currents and responsivities of the devices will decrease with the increasing electrode spacing at the same bias. It was thought that the resistance and the depletion region between the electrodes play important roles in the devices, and the physical mechanism can be explained by a straightforward qualitative model.