Metal-semiconductor-metal Photodiodes Research Articles

Growth of III-nitrides on Si(111) and its application to photodiodes

In this paper, we investigated growth of GaN and Al0.09Ga0.91N epilayer grown on silicon (111) by using II MBE system. The major characterization tools used for this study were high resolution X-ray diffraction (HRXRD), and micro photoluminescence (PL) spectroscopy. Also reported is our attempt to fabricate and characterize metalsemiconductor-metal photodiode based on these films. The responsivity as a function of wavelength for an MSM GaN/Si(111) detector is a sharp cut-off wavelength at 362 nm. A maximum responsivity of 0.256 A/W was achieved at 358 nm. For Al0.09Ga0.91N film, there is a sharp cut-off wavelength at 340 nm. A maximum responsivity of 0.263 A/W was achieved at 338 nm. In UV spectral region, the detector shows a little decrease from 340 to 200 nm. The responsivity of the MSM drops by nearly an order of magnitude across the cut-off wavelength.

Dramatically Enhanced Efficiency in Ultra-Fast Silicon MSM Photodiodes Via Light Trapping Structures

Due to relatively low responsivity at near infrared (NIR) wavelengths, surface-illuminated silicon (Si) photodiodes (PDs) are not attractive for ultra-fast data communication applications despite their CMOS-compatibility. Metal-semiconductor-metal (MSM) photodiodes are well-known for simplicity in fabrication compared to pin and pn junctions-based counterparts, but they usually work with lower efficiencies due to thin absorption layer that ensures high speed response. In this letter, we demonstrate a high efficiency and high-speed Si MSM PD with innovative photon-trapping surface structures. These wavelength-scale structures decrease the surface reflection and introduce laterally propagating waves parallel to the semiconductor surface. The responsivity of Si MSM PDs with the photon-trapping holes was measured to be ~0.59A/W, while the control devices without holes show ~0.08A/W. Such PDs with $50\mu \text{m}$ diameter and with 1 $\mu \text{m}$ finger spacing provide a pulse response of 60ps and 38ps full-width at half-maximum (FWHM) at 3V and 10V applied bias, respectively. Surface-illuminated PDs with these dimensions can offer easy optical coupling options for fiber optic links while offering complete CMOS compatibility.

InGaN-Based MSM Visible Light Photodiodes With Recessed Anode

In0.17Ga0.83N-based metal-semiconductor-metal photo-diodes (MSM-PDs) with recessed anode electrodes were fabricated and characterized. The photodiodes exhibited low dark current of $8\,\times \, 10^{-12}$ A at 5 V, which was one order lower than that of the conventional planar MSM-PDs. Peak responsivity up to 0.22 A/W was obtained at 430 nm and 1.5 V, corresponding to an external quantum efficiency of 63%. The 440 nm/490 nm rejection ratios of the recessed and planar MSM-PDs were ~103 and 102, respectively. The improvements were attributed to the suppression of lateral surface leakage current and the enhancement of the internal electric field by the recessed anode electrodes.

AlGaN Ultraviolet Metal–Semiconductor–Metal Photodetectors with Reduced Graphene Oxide Contacts

AlGaN semiconductors are promising materials in the field of ultraviolet (UV) detection. We fabricated AlGaN/GaN UV metal–semiconductor–metal (MSM) photodiodes with two back-to-back interdigitated finger electrodes comprising reduced graphene oxide (rGO). The rGO showed high transparency below the wavelength of 380 nm, which is necessary for a visible-blind photodetector, and showed outstanding Schottky behavior on AlGaN. As the photocurrent, dark current, photoresponsivity, detectivity, and cut-off wavelength were investigated with the rGO/AlGaN MSM photodiodes with various Al mole fractions, systematic variations in the device characteristics with the Al mole fraction were confirmed, proving the potential utility of the device architecture combining two-dimensional materials, rGO, and nitride semiconductors.

Effects of annealing treatment on the high temperature performance of 4H-SiC metal-semiconductor-metal ultraviolet photodiodes

The high temperature performance plays a crucial role in the high-temperature harsh environment detection. In this paper, the electrical and optical characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet photodiodes (PDs) were investigated at high temperatures. The C-V measurement indicates that the 4H-SiC Schottky barrier diode is partially depleted at 40V bias. Analysis of I-V data based on the thermionic emission theory demonstrates that the annealing treatment at 400°C can effectively improve the homogeneity of Ni/4H-SiC Schottky barrier height. Experimental results confirm that the annealing treatment is beneficial not only to reduce the dark current and improve the photoresponse, but also to enhance the sensitivity for 4H-SiC MSM PDs. The sensitivity of 400°C annealed MSM PDs (6.2 × 103) is five times larger than that of as-deposited MSM PDs (1.3 × 103) at 200°C.

Flexible metal-semiconductor-metal device prototype on wafer-scale thick boron nitride layers grown by MOVPE

Practical boron nitride (BN) detector applications will require uniform materials over large surface area and thick BN layers. To report important progress toward these technological requirements, 1~2.5 µm-thick BN layers were grown on 2-inch sapphire substrates by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties were carefully characterized and discussed. The thick layers exhibited strong band-edge absorption near 215 nm. A highly oriented two-dimensional h-BN structure was formed at the film/sapphire interface, which permitted an effective exfoliation of the thick BN film onto other adhesive supports. And this structure resulted in a metal-semiconductor-metal (MSM) device prototype fabricated on BN membrane delaminating from the substrate. MSM photodiode prototype showed low dark current of 2 nA under 100 V, and 100 ± 20% photoconductivity yield for deep UV light illumination. These wafer-scale MOVPE-grown thick BN layers present great potential for the development of deep UV photodetection applications, and even for flexible (opto-) electronics in the future.

Fabrication and characterization of In0.83Al0.17N based MSM visible photodiode

In this work, we report on the growth of In 0.83 Al 0.17 N film on p -type Si (1 1 1) substrate for metal-semiconductor-metal (MSM) photodiode application. The film was synthesized by reactive magnetron co-sputtering technique on Si (1 1 1) substrate in Ar and N 2 mixture at 300 °C. The X-ray diffraction analysis revealed (0 0 2) oriented diffraction peak corresponding to nanocrystalline InAlN. The band gap of In 0.83 Al 0.17 N film was estimated from UV-vis reflectance measurement and it was found to be 2.38 eV. To fabricate In 0.83 Al 0.17 N based MSM photodiode, Pt contacts were deposited on the film through RF magnetron sputtering. Upon exposure to 520 nm light, the Pt/In 0.83 Al 0.17 N/Pt photodiode displayed a sharp rise in the value of current. The photodiode exhibited a high sensitivity (4.8×10 3 ) and current gain (48.1) at a bias voltage of 5 V. The response and recovery time were calculated to be 0.62 and 0.63 s respectively. The results of present work demonstrate that the sputtered grown InAlN film is a promising material for the MSM photodiode application.

Visible Light-Assisted High-Performance Mid-Infrared Photodetectors Based on Single InAs Nanowire.

One-dimensional InAs nanowires (NWs) have been widely researched in recent years. Features of high mobility and narrow bandgap reveal its great potential of optoelectronic applications. However, most reported work about InAs NW-based photodetectors is limited to the visible waveband. Although some work shows certain response for near-infrared light, the problems of large dark current and small light on/off ratio are unsolved, thus significantly restricting the detectivity. Here in this work, a novel "visible light-assisted dark-current suppressing method" is proposed for the first time to reduce the dark current and enhance the infrared photodetection of single InAs NW photodetectors. This method effectively increases the barrier height of the metal-semiconductor contact, thus significantly making the device a metal-semiconductor-metal (MSM) photodiode. These MSM photodiodes demonstrate broadband detection from less than 1 μm to more than 3 μm and a fast response of tens of microseconds. A high detectivity of ∼1012 Jones has been achieved for the wavelength of 2000 nm at a low bias voltage of 0.1 V with corresponding responsivity of as much as 40 A/W. Even for the incident wavelength of 3113 nm, a detectivity of ∼1010 Jones and a responsivity of 0.6 A/W have been obtained. Our work has achieved an extended detection waveband for single InAs NW photodetector from visible and near-infrared to mid-infrared. The excellent performance for infrared detection demonstrated the great potential of narrow bandgap NWs for future infrared optoelectronic applications.

Cupric and cuprous oxide by reactive ion beam sputter deposition and the photosensing properties of cupric oxide metal–semiconductor–metal Schottky photodiodes

Cupric (CuO) and cuprous (Cu2O) oxide thin films have been deposited by reactive ion beam sputter deposition at 400°C with an Ar:O2 ratio from 2:1 to 12:1. With an Ar:O2 ratio of 2:1, single phase polycrystalline CuO thin films were obtained. Decreasing oxygen flow rate results in CuO+Cu2O and Cu2O+Cu mixed thin films. As Ar:O2 ratio reaches 12:1, Cu2O nanorods with diameter of 250nm and length longer than 1μm were found across the sample. Single phase CuO thin film exhibits an indirect band gap of 1.3eV with a smooth surface morphology. CuO metal–semiconductor–metal (MSM) Schottky photodiodes (PD) were fabricated by depositing Cu interdigitated electrodes on CuO thin films. Photosensing properties of the CuO PD were characterized from 350 to 1300nm and a maximum responsivity of 43mA/W was found at λ=700nm. The MSM PD is RC limited with a decay time constant less than 1μs.

A comparative study of IR Ge photodiodes with a Schottky barrier contact and metal-semiconductor-metal structure

We report the characterization of germanium (Ge) infrared photodiodes fabricated with a Schottky barrier contact and a interdigitated metal-semiconductor-metal (MSM) structure with gold electrodes on n-Ge substrates. The current-volage (I-V) characteristics were studied, and parameters such as the ideality factor and the barrier height of the Schottky contacts were extracted. Furthemore, we estimated the dark current and the photocurrent under illumination with λ = 1550 nm light, and we measured the capacitance-voltage (C-V) characteristics and the dependence of the responsivity on the bias voltage of both photodiodes at room temperature. The dark currents of the Schottky and the MSM photodiodes were ~ 20.2 μA and ~ 26.0 μA under −1 V bias and −2 V bias, respectively. In addition, the reverse breakdown voltage was high, in excess of ~ −30 V. The Schottky barrier height was deduced to be 0.546 eV. A maximum responsivity of 0.27 A/W was achieved under illumination with λ = 1550 nm light at a 2-V bias. A typical peak was observed at a wavelength of 1600 nm, and a high responsivity was observed in the wavelength range from 1200 to 1800 nm.

Nickel on porous silicon MSM photo-detector and quantum confinement in nanocrystallites structure as methods to reduce dark current

We propose in this work, contact Schottky Nickel/porous silicon (PSi) system, coupled to nanocrystallites size variation of material for a possible technique to reduce dark current. The device consists of metal- semiconductor-metal photodiode (MSM-PD). Higher barrier Φ Β enhances the performance of MSM-PD through reduction in dark current (Is), and benefits to resolve noise from signal detection of the devices. In order to reduce much more Is, we proposed different anodization times (5–7–10 min) as method to tune the size of nanocrystallites. As result Is value was reduced to almost two orders of magnitude for 10 min etching time, and the value of I s ≈ 10 –10 A. Φ Β reached the value of 0.882 eV. Among the hypothesis suggested in the reduction of I s was the quantum confinement effects. According to Rhoderick model, the Schottky barrier height is explicitly linked to the band gap energy due to the presence of interface states. The existence of narrow nanocrystallites increased energy band gap of PSi and the Schottky barrier height, which in turn reduces I s. The photoluminescence measurements confirmed our hypothesis. Photosensitivity of the device was established by adopting the MSM configuration, and strong absorption was detected in visible range.

Preparation and Characterizations of the High UV Sensitivity Porous Diamond-Like Carbon Thin Film MSM Photodiodes

For the first time, we use a porous diamond-like carbon (DLC) film formed on a porous Si substrate to promote its ultraviolet (UV) quantum efficiency. With the porous DLC films, we developed metal-semiconductor-metal (MSM) photodiodes for UV detecting applications. The morphology and structure of the porous DLC film were analyzed with SEM photos for both top and cross section views. Besides, we examined the responses of the diodes to UV light by measurement of the photo/dark current ratio with and without the irradiation of a 366 nm UV light. Experiments show the current ratio and quantum efficiency are respectively promoted ~570% and ~76% under -15 V bias by the porous structure.

GaN ON SILICON SUBSTRATE WITH AlN BUFFER LAYER FOR UV PHOTODIODE

Nitrogen plasma-assisted molecular beam epitaxy (PAMBE) deposited GaN thin films on (111) n-type silicon substrate with different thickness AlN buffer layers are investigated and distinguished by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman scattering. The thickness of AlN buffer layer ranged from 200 nm to 300 nm. Besides that, the electrical characteristics of the GaN thin film for ultraviolet detecting utilizations are studied by calculating the photo current/dark current ratio on a metal-semiconductor-metal (MSM) photodiode with and without the illumination of Hg-lamp source. The devices have been tested over room temperature (RT). The photocurrent analysis, together with the study of Schottky barrier height (SBH) development, ascertain that the principal mechanism of photo transport is thermionic emission. The photocurrent value is rigorously dependent on Schottky barrier height. The GaN/AlN(200 nm)/n-Si MSM photodiode produces the highest photo/dark current ratio for the lowest strain that consists of the GaN film grown on the AlN (200 nm) buffer layer.

An Optical Input Module With Superconducting Single-Flux-Quantum Circuit Operating at 1550 nm

We developed an optical input module consisting of built-in metal-semiconductor-metal photodiodes (MSM-PDs) and co-planar waveguide transmission lines fabricated on an InP substrate, which is flip-chip bonded with a single-flux-quantum (SFQ) circuit fabricated on a Si substrate. To improve photosensitivity of the MSM-PD for a wavelength above 1530 nm at 4 K, we tested the MSM-PDs made of lattice mismatched In1-xGaxAs films on InP substrates. By employing In1-xGaxAs with x=0.44, an apparent reduction of photosensitivity for a wavelength above 1530 nm was suppressed. We also tested newly designed DC/SFQ converters with higher input current sensitivities. The observed current sensitivity was improved to 41 μA, while that in the conventional DC/SFQ converter was 140 μA.

Performance improvement of large area GaN MSM photodiode with thin AlGaN surface layer

PurposeThe purpose of this paper is to propose a new structure of GaN based metal‐semiconductor‐metal (MSM) photodiode, in which a thin unintentionally doped n‐type AlGaN layer is added on the conventional GaN on Si(111) device structure.Design/methodology/approachA thin Al0.50Ga0.50N cap layer of 100 nm was incorporated in GaN MSM photodiode to enhance the effective Schottky barrier height and reduce the dark current. When the incident light with photon energy higher than the band edge of GaN but lower than the bandgap of AlGaN illuminates the front face of photodiode, the light can be transparent in the top AlGaN layer and is only absorbed by the GaN layer. As a result, the photogenerated carriers in the GaN layer would be influenced by the interface states of AlGaN/GaN. It is known that the density of the interface states is normally lower than that of surface states, so the recombination of photogenerated electron‐hole pairs will be reduced. A barrier height of 0.54 eV for normal GaN MSM photodiode was increased to the effective barrier height of 0.60 eV.FindingsThe resulting MSM photodiode shows a dark current of as low as 8.0×10−4 A at 5 V bias, which is about two orders of magnitude lower than that of normal GaN (1.0×10−2 A at 5 V bias) MSM photodiode.Originality/valueThe paper reports on barrier enhanced GaN Schottky MSM photodiode using a thin AlGaN cap layer. AlGaN cap layers were found to effectively suppress the leakage current of the GaN Schottky MSM photodiode, resulting in improved device characteristics. The dark current for the Schottky contact with the AlGaN cap layer was shown to be about about two orders of magnitude smaller than that of conventional GaN Schottky MSM photodiode.

GaN on Silicon Substrate With Various SiC Buffer Layer for UV Detecting Applications

Metal organic chemical vapor deposited Gallium nitride (GaN) thin films on (111) n-Si substrate with polycrystalline β-SiC (poly-SiC), cubic β-SiC (c-SiC), and porous β-SiC (PSC) buffer layers were characterized in detail using X-ray diffraction, Fourier transform IR spectroscopy, atomic force microscope, TEM, SEM, and Raman spectrometer. The β-SiC thin film was prepared by rapid thermal chemical vapor deposition, while the PSC thin film was formed by using the electrochemical anodization on a cubic β-SiC thin film. In addition, we used the GaN thin film on different buffer layers to construct a metal-semiconductor-metal (MSM) photodiode and measured its photo/dark current ratio (PDCR) and responsivity with and without the irradiance of an UV light source for examining the ultraviolet detecting properties. Among these MSM photodiodes, the structure of GaN/PSC/n-Si achieved the highest PDCR and responsivity of 6.75 × 105 and 138 mA/W, respectively, for the lowest stress built in the GaN film.

Comparison of Performance of Integrated Photodetectors Based on ZnS and ZnSe Metal–Semiconductor–Metal Photodiodes

The successful fabrication of monolithically integrated photodetectors composed of a heterojunction bipolar transistor (HBT) and a metal–semiconductor–metal (MSM) photodiode was achieved by a patterned oxide growth technique. The photoresponsivities of the ZnS and the ZnSe MSM photodiodes were 0.028 and 0.08 A/W, respectively. Comparison of the performance in terms of optical and electrical characteristics between the ZnS- and the ZnSe-based integrated photodetectors were carried out; at a bias of 5 V, the current amplification ratios were 18.2 and 20.8, respectively. The maximal measurable input optical power intensities were 273 µW for ZnS-based integrated photodetector and 94 µW for ZnSe-based integrated photodetector. This successful integration indicates the potential of the patterned oxide growth technique in the development of integrated devices based on II–VI ZnS and ZnSe compounds for short-wavelength applications.

Integrated a ZnSe MSM Photodiode and an InGaP/GaAs HBT on a GaAs Substrate for High Sensitivity Short Wavelength Photodetector

A ZnSe MSM photodiode and an InGaP/GaAs HBT have been integrated successfully on a GaAs substrate by use of the selective-area epitaxy technique. The optical and electrical characterizations of the integrated photoreceiver as well as individual components used in this device structure were estimated. Photocurrent induced from the metal-semiconductor-metal (MSM) photodiode was amplified linearly by a common-emitter circuit composed of a HBT. A current amplification ratio and a voltage amplification sensitivity of the integrated device measured in this work were 20.8 and -29.6 mV/mu W, respectively. The result does not only demonstrate the high sensitivity monolithic photoreceiver but indicates the potential of the selective-area epitaxy technique in the development of WBG-based short wavelength integrated devices.

Optical sensor with transparent conductive oxides electrodes for microposition detection applications

This paper presents an optical sensor structure for microposition detection application using transparent electrodes of indium doped ZnO (IZO). The optical microsensor consists of two linear arrays of metal – semiconductor – metal (MSM) silicon photodetectors with IZO transparent electrodes integrated with a polymer optical waveguide. IZO layers with a thickness of 460–580 nm have been deposited by dc magnetron sputtering technique on silicon epitaxial wafers of 30–50 Ω cm resistivity and a thickness of 23 µm. Due to their high optical transmittance (> 90%) over the 0.4–0.9 µm spectral range, these layers contributed to an increased responsivity of the MSM photodiode structure of about 0.34 A/W, thus improving the optical position microsensor sensitivity.

High‐quality In0.47Ga0.53N/GaN heterostructure on Si(111) and its application to MSM detector

PurposeThis paper aims to report on the use of radio frequency nitrogen plasma‐assisted molecular beam epitaxy (RF‐MBE) to grow high‐quality n‐type In0.47Ga0.53N/GaN on Si(111) substrate using AlN as a buffer layer.Design/methodology/approachStructural analyses of the InGaN films were performed by using X‐ray diffraction, atomic force microscopy, and Hall measurement. Metal‐semiconductor‐metal (MSM) photodiode was fabricated on the In0.47Ga0.53N/Si(111) films. Electrical analysis of the MSM photodiodes was carried out by using current‐voltage (I‐V) measurements. Ideality factors and Schottky barrier heights for Ni/In0.47Ga0.53N, was deduced to be 1.01 and 0.60 eV, respectively.FindingsThe In0.47Ga0.53N MSM photodiode shows a sharp cut‐off wavelength at 840 nm. A maximum responsivity of 0.28 A/W was achieved at 839 nm. The detector shows a little decrease in responsivity from 840 to 200 nm. The responsivity of the MSM drops by nearly two orders of magnitude across the cut‐off wavelength.Originality/valueFocuses on III‐nitride semiconductors, which are of interest for applications in high temperature/power electronic devices.