High-gain Photodetector Research Articles

A high-gain, modulation-doped photodetector using low-temperature MBE-grown GaAs

We report the fabrication and performance of a novel, high gain photodetector. Basically, the device is a modulation-doped field effect transistor (MODFET) structure with its channel region made of low-temperature MBE-grown GaAs. It exhibits an excellent responsivity of 65 A/W at /spl sim/0.87 μm and 6.5 A/W at /spl perp/1.0 μm. In the sub-bandgap range (0.9-1.3 μm) the responsivity of this device is the highest ever reported, to our knowledge, for any GaAs-based device. Thus, the device appears to be ideally suited for applications requiring a high photodetection sensitivity, especially in the 1.3 μm wavelength region. Charge separation by the built-in field normal to the heterojunction plane is attributed to be responsible for the gain in the device.

Characteristics of a single a-SiC : H/a-Si : H heterostructure as a high-gain photodetector

This paper describes a structure for the hydrogenated amorphous-silicon (a-Si : H) based photodetector having high optical gain. This structure consists of a single heterostructure of hydrogenated amorphous-silicon carbide (a-SiC : H) and a-Si : H. The operation of this photodetector is based on the multiplication of the photoinduced carriers in a-SiC : H layer. the photocurrent multiplication is dependent on the optical band-gap of the a-SiC : H used, and with the use of 2.35 eV a-SiC : H, its multiplication is reached to 9 at the bias voltage of 20. The leakage current and the response-speed of this photodetector were also less than 10 nA/cm 2 and 0.5 μs, respectively, under the reverse-bias of 20 V.

Effective mass filtering: Giant quantum amplification of the photocurrent in a semiconductor superlattice

We report the first observation of an extremely large photocurrent amplification phenomenon at very low voltages in a superlattice of Al0.48In0.52As (35 Å)/Ga0.47In0.53As (35 Å), grown by molecular beam epitaxy. Responsivities at λ=1.3 μm are as high as 4×103 A/W at 1.4 V corresponding to a current gain of 2×104. Significant gains (≂50) were obtained at voltages as low as 20 mV. The detectivity D* at λ=1.3 μm and 1-kHz modulation frequency is 1011 (cm Hz1/2/W) at 0.2-V bias. This effect, which represents a new quantum type photoconductivity, is caused by the large difference in the tunneling rates of electrons and holes through the superlattice barriers, associated with their large effective mass difference (effective mass filtering). Superlattice effective mass filters represent a new class of low voltage, high gain photodetectors. A unique feature, which makes them potentially extremely versatile, is the ability to tune the gain and gain-bandwidth product over a wide range by varying the superlattice period and/or duty factor.

High-gain photodetectors in thin-film transistors fabricated from laser-crystallized silicon on fused silica

We report the achievement of high-gain photoconduction in transistors fabricated in laser-crystallized silicon thin films on fused silica with responsivities of about 300 A/W for radiation in the visible spectrum. Such photodetectors are potentially useful in page-width linear document input scanners with higher speed and resolution than possible with other thin-film sensor arrays. The basic mechanism for photoconductivity consists of spatial separation of photogenerated electron-hole pairs across a p-n junction in the device body, collection of holes in the floating substrate, and ohmic conduction of electrons in a buried channel. This model predicts a long carrier lifetime and is verified by a photocurrent decay time of about 10-100 µs.

Analysis of high-speed and high-gain n -InP transferred electron effect photodetector

By illuminating the small area of the semitransparent Schottky barrier cathode of an n-InP diode with above-bandgap radiation, the travelling dipole domain can be triggered. The dipole domain transversely extends with a velocity of 108 cms−1. The nature of high travelling speed and high extension speed of the dipole domain can be used for achieving a high-speed and high-gain n-InP photodetector.

<title>A Fiber Optic Time Domain Reflectometer</title>

An optical time domain reflectometer is described which combines in one instrument the basic capability to analyze several important fiber characteristics. The device uses the polarization properties of light to enable high sensitivity fault detection close to the fiber input end; its probe pulse temporal characteristics and high gain photodetector in combination provide excellent discontinuity location resolution in long lossy fibers, and give an indication of fiber dispersion at large bandwidths.

An optimized avalanche photodiode

The feasibility of a fast, high-gain photodetector based on the phenomenon of avalanche multiplication in semiconductors has been investigated. Based on the process of carrier multiplication in a high electric field, criteria for the design of an optimized avalanche photodiode and for the choice of the best semiconductor material are developed. The device theory of an optimized, realizable avalanche photodiode is presented. A practical silicon device optimized for the detection of light with a wavelength of 9000Å is suggested and design parameters are presented. Details of the fabrication process are given and the performance of experimental devices is compared to the device theory presented. The results of the study indicate that it is possible to achieve a silicon photomultiplier with a quantum efficiency-bandwidth product of the order of 100 GHz for the detection of light up to a wavelength of over 9000Å.