Low dark current GaAs metal-semiconductor-metal (MSM) photodiodes using WSixcontacts

We present the fabrication and characterization of metal-semiconductor-metal (MSM) photodiodes using the same undoped GaAs layer that is used as a buffer layer in the epitaxial structure for GaAs field effect transistors (FET's). To study the dark current mechanism, various metal electrodes used for Schottky contacts are examined. A drastic V-shape relationship between the dark current of MSM photodiode and the Schottky barrier height is found. An extremely low dark current (a few nanoamperes) in the MSM photodiode is obtained by using tungsten silicide as electrode metal. It is concluded that the dark current is a function of a rivalry relation between the electron injection at the cathode and the hole injection at the anode. The internal gain of the MSM photodiode with tungsten silicide contacts is found, and possible mechanisms are discussed. A flat frequency response up to 1.3 GHz is obtained. The results shows the feasibility of MSM photodiodes for use as photodetectors with low minimum detectable power, and their applicability to monolithic integration with FET circuits.     

Lateral high-speed metal-semiconductor-metal photodiodes onhigh-resistivity InGaAs

First results are presented on the fabrication and characterization of MSIM photodetectors on high-resistivity Fe-doped InGaAs. The acronym MSIM refers to the fact that the active layer of the photodiodes consists of a semi-insulating (SI) photoabsorbing semiconductor layer. Metal-semiconductor-metal (MSM) photodetectors on high-resistivity InGaAs with a lateral planar structure have been fabricated and characterized. The detectors formed exhibit a low capacitance (<50 fF), a very fast response (>14 GHz), a dark current of about 250 nA at a bias voltage of 10 V, and an external quantum efficiency of 20% at 1.3 μm. The dark current values of the MSIM devices are only a factor of three larger than the values for MSM photodetectors based on a technologically complex AlInAs/InGaAs superlattice. This result indicates that the Fe doping of the photoactive InGaAs layer yields a significantly increased Schottky barrier. The fabrication of MSM photodetectors on high-resistivity InGaAs is demonstrated. Laterally structured photodiodes are formed with interdigitated contact fingers. The devices show a high response bandwidth and are suitable for high-speed applications     

A monolithic four-channel photoreceiver integrated on a GaAs substrate using metal-semiconductor-metal photodiodes and FET's

The first fabrication of a monolithic four-channel photoreceiver on a GaAs substrate, using metal-semiconductor-metal (MSM) photodiodes and GaAs metal-semiconductor field-effect transistors (MESFET's) is described. The present photoreceiver operating in the 0.8- µm wavelength region has shown uniform sensitivity with little crosstalk between channels and also giga-bit response. The result suggests that the use of MSM photodiodes and FET's has good expansibility toward high-density and multi-channel monolithic integration.     

High-speed InGaAs on Si metal-semiconductor-metal photodetectors

High-speed long-wavelength metal-semiconductor-metal (MSM) photodetectors were fabricated on the Fe-doped InP/GaAs material system on Si. The detector layers were grown by MOCVD on exactly oriented Si(001) patterned with submicrometre pitch V-grooves. The devices show a fast impulse response (44 ps FWHM, 83 ps fall time) and a large bandwidth of 3.4 GHz for illumination with 1.31 μm light pulses at 5 V bias     

Mesa-isolated GaAs Schottky-barrier photodiodes

The design, fabrication and characterisation of GaAs Schottky-barrier photodiodes with evaporated, free-standing-metal airbridges is reported. The photodiodes were fabricated using all dry-etching techniques. Anisotropic chemically assisted ion beam etching was used to etch vertical sidewall mesas, and isotropic reactive ion etching was used to etch a lateral tunnel. A free-standing-metal airbridge created by the lateral tunnel etch results in isolation of the active area at the same time providing free-standing-metal interconnection to the contact pad.<>     

High-speed metal-semiconductor-metal photodetectors on InP:Fe

Metal-semiconductor-metal (MSM) photodetectors on semi-insulating InP:Fe with a lateral planar structure have been fabricated. Laterally structured photodiodes are formed with interdigitated contact fingers. The detectors exhibit low dark currents of about 10 nA, an impulse response of 26 ps FWHM (full-width of half-maximum), and an internal quantum efficiency of 80%, all at 10 V bias. An electrical cutoff frequency of 40 GHz for the packaged detectors is obtained from s -parameter measurements, demonstrating that the response time is not limited by the parasitic elements of the devices     

High-gain GaAs avalanche photodiodes with proton-implanted guard ring

A GaAs avalanche photodiode with a multiplication factor as high as 8000 was prepared by Zn diffusion and proton double implantation. The proton-implanted guard ring completely prevented edge breakdown, and multiplication occurred uniformly over the junction area. Dark current was proved to be due to a leakage current at the periphery between junction and implanted layer.     

Studies of high-speed metal-semiconductor-metal photodetector witha GaAs/AlGaAs/GaAs heterostructure

A GaAs/AlGaAs/GaAs heterostructure metal-semiconductor-metal photodetector (HMSM) with an active area of 100 μm×100 μm was developed and studied. The measured risetime of the device is 30 ps. The measured falltime is as short as 23 ps. The observed ultrafast response is attributed to the reduction of both the carrier transit time and the device capacitance due to the incorporation of the AlGaAs barrier layer. The HMSM is found to have a smaller saturation capacitance and saturates at a much lower bias voltage in comparison with the conventional MSM photodetector (CMSM). At a bias of 10 V, the full width at half maximum (FWHM) of the temporal response of the HMSM is more than 20% smaller than that of the CMSM. In addition, it is found that the peak impulse response for the HMSM is substantially larger than that of the CMSM under the same operation condition. Two-dimensional and equivalent circuit analyses were carried out to interpret the observed phenomena and to provide insight into the underlying physics     

Performance of a near-infrared GaAs metal-semiconductor-metal (MSM)photodetector with islands

A GaAs metal-semiconductor-metal (MSM) photodetector with ultrasmall gold islands deposited on its photosensitive surface is described. The interdigitated detector is fabricated on a semi-insulating substrate in a MESFET-compatible technology. Responsivity as high as 1.8 A/W is obtained at 0.86 μm and a bias voltage of 8 V. This represents over a sixfold increase with respect to responsivity of a conventional MSM photodetector. The mechanism for dark current is suggested and breakdown characteristics are presented     

Excess noise in GaAs avalanche photodiodes with thin multiplicationregions

It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP-InGaAsP-InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This paper presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite “size effect” for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process     

Photocurrent multiplication in GaAs Schottky photodiodes

Many attempts have been made to build fast, sensitive photodetectors which offer simple fabrication and ease of integration. Regarding this view, GaAs Schottky barrier photodiodes seem to be ideally suited for use in the near-infrared region. The fabrication of GaAs Schottky photodiodes and the investigation of their properties (mainly photocurrent multiplication) are presented in this paper. A photocurrent gain of 10⁴ was achieved and dependences of gain on incident power level and position were observed.     

High-speed integrated logic with GaAs MESFET's

The feasibility of using GaAs metal-semiconductor field-effect transistors (GaAs MESFET's) in fast switching and high-speed digital integrated circuit applications is demonstrated. GaAs MESFET's with 1-/spl mu/m gate length are shown to have a current-gain-bandwidth product f/SUB T/ equal to 15 GHz. These devices exhibit a 15 ps internal delay in a large-signal switching test. A simple logic circuit consisting of MESFET's and Schottky diodes was monolithically integrated on a semiinsulating GaAs substrate. This logic circuit exhibits a propagation delay of 60 ps with no output load, and 105 ps when its output is loaded by three similar logic gates. A useful bandwidth of approximately 3 GHz is observed.     

Dark current characteristics of GaAs metal-semiconductor-metal(MSM) photodetectors

Calculations of the electron and hole components of dark current in a GaAs metal-semiconductor-metal (MSM) photodetector are presented. A quantum-mechanical model for the electron and hole transport behavior in the contact regions which is used to determine dark current as a function of electric field is developed. The model reduces to a conventional thermionic emission model if an ideal barrier transmission coefficient is assumed. In order to assess the accuracy of the model, photodetectors have been fabricated and tested. Theoretical calculations and experimental data are compared, and good agreement is obtained. Possible modifications to enhance the usefulness of the model are discussed     

High-speed InP/InGaAs avalanche photodiodes with a compositionallygraded quaternary layer

InP/InGaAs avalanche photodiodes (APDs) with a compositionally graded quaternary layer at the heterointerface between the InGaAs absorption and InP multiplication regions were fabricated and tested. A comparison of samples with the graded layer and with conventional three quaternary layers showed that the frequency characteristics for samples with the graded layer did not deteriorate at a low bias voltage even below -100°C, unlike APDs with three InGaAsP layers. Thus, no hole trapping occurred at the InP/InGaAs heterointerface with the graded layer. A sample with the graded layer showed a cutoff frequency exceeding 9 GHz at a low multiplication factor of 2. The authors found InP/InGaAs APDs with the compositionally graded quaternary layer to be useful over a wide temperature range     

High-speed frequency dividers with quasi-normally-off GaAs MESFETs

Master-slave binary frequency dividers have been designed and implemented with enhancement-mode GaAs MESFETs by using the so-called LPFL logic approach. A wide range of speed-power performances has been observed: a maximum toggle frequency of 2.8 GHz at P = 15 mW/gate on a dual-clocked frequency divider and an fc,max of 1.73 GHz at Pxtpd = 1 pJ/gate on a single-clocked one. The high-speed performance obtained corresponds to a propagation delay of 145 ps for the constituent NOR-OR gates of fan-in/fan-out = 4/3, and it is made possible by careful optimisation of circuit design parameters.     

High-speed limitations of the metal-semiconductor-metal photodiode structures with submicron gap between the interdigitated contacts

Impulse response of metal-semiconductor-metal photodetector (MSM-PD) to a short light pulse is computed and discussed in terms of the distribution of photogenerated carriers and electric fields. A two-dimensional self-consistent time-dependent technique has been applied to investigate carrier drift processes in the active volume of high-speed MSM-PD structures with small contact separation. We analyze the limitations imposed by reduced dimensions of the interdigitated electrode system of the MSM-PD. We show that the heterobarrier structure in the light-absorbing region greatly affects the movement of optically generated carriers and enhances the response speed of InP/GaInAs MSM-diode.     

High-speed GaAs SCFL divider

A single-clocked divide-by-four circuit with a maximum operating frequency of 5.2 GHz has been developed. The circuit was fabricated using 1 ?m-gatelength high-transconductance enhancement-mode GaAs MESFETs with Pt-buried gate structure. The basic building block of the circuit is a source-coupled FET logic (SCFL) master-slave flip-flop with ECL-compatible input and output.     

High-speed GaAs operational amplifier

An operational amplifier has been designed and fabricated using GaAs MESFETs. This amplifier is a general-purpose monolithic GaAs op amp designed as as a stand-alone component. The amplifier has a differential input, an open-loop gain in excess of 60 dB, and is internally compensated. The high open-loop gain (60 dB at 100 kHz) was achieved by using gain stages with positive feedback. The op amp incorporates a current-mirror level-shifting stage which allows the op amp to operate over a wide power-supply range (/spl plusmn/5-9 V). Previous designs have diodes to achieve level shifting, a practice that precludes operation over a wide supply range. This op amp is a true analog to its silicon counterparts, but it has a higher gain-bandwidth product.     

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 40 V 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.     

P-down ZnSTeSe/ZnSe/GaAs heterostructure photodiodes

High-quality quaternary ZnSTeSe epitaxial layers with uniform carrier concentration of 1/spl times/10/sup 17/ cm/sup -3/ were successfully grown on p-GaAs substrates by molecular beam epitaxy. P-down ZnSTeSe/ZnSe/GaAs heterostructure photodiodes were also fabricated. It was found that the maximum quantum efficiency of the fabricated ZnSTeSe photodiodes was around 75% with a large spectral width of 500 nm.