No abstract

Photodetectors fabricated on microstructured silicon are reported. The photodetectors exhibited high photoresponse; at 3V bias, the responsivities were 92A∕W at 850nm and 119A∕W at 960nm. At wavelengths longer than 1.1μm, the photodetectors still showed strong photoresponse. A generation-recombination gain mechanism has been proposed to explain the photoresponse of these photodiodes. From measurements of the noise current density, the calculated gain was approximately 1200 at 3V bias.

We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic “punch-through” voltage, which we attribute to the interaction of the depletion region with the underlying low-temperature buffer layer. We also report GaN metal–semiconductor–metal photodetectors with high quantum efficiencies (∼50%) in the absence of internal gain. These photodetectors have a flat responsivity above the band gap (measured at ∼0.15 A/W) with a sharp, visible-blind cutoff at the band edge. There is no discernible responsivity for photons below the band-gap energy. We also obtained record low dark current of ∼800 fA at −10 V reverse bias. The dark current and ultraviolet photoresponse I–V curves are very flat out to VR>−25 V, and do not show evidence of trap-related degradation, or punch-through effects.

Articles you may be interested inHigh-detectivity InAs quantum-dot infrared photodetectors grown on InP by metal-organic chemical-vapor deposition Appl. Phys. Lett. 86, 191103 (2005); 10.1063/1.1923176 High-performance 30-period quantum-dot infrared photodetectorInfluence of rapid thermal annealing on a 30 stack InAs/GaAs quantum dot infrared photodetector

For high-bit-rate long-haul fiber optic communications, the avalanche photodiode (APD) is frequently the photodetector of choice owing to its internal gain, which provides a sensitivity margin relative to PIN photodiodes. APDs can achieve 5-10-dB better sensitivity than PINs, provided that the multiplication noise is low and the gain-bandwidth product is sufficiently high. In the past decade, the performance of APDs for optical fiber communication systems has improved as a result of improvements in materials and the development of advanced device structures. This paper presents a brief review of APD fundamentals and describes some of the significant advances.

In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric field and the new one. A systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses is also presented. It is demonstrated that there is a definite "size effect" for thin multiplication regions that is not well characterized by the local-field model. The new theory, on the other hand, provides very good fits to the measured gain and noise. The new ionization coefficient model has also been validated by Monte Carlo simulations.

No abstract

We have performed a comprehensive investigation of n-type quantum dot infrared photodetectors ͑QDIPs͒ based on InAs/GaAs epitaxical island quantum dots ͑QDs͒ grown via the innovative punctuated island growth technique. The structural properties of the QDs were investigated with cross-sectional transmission electron microscopy and atomic force microscopy. The electronic properties of the QDs inserted in QDIP devices were investigated with photoluminescence ͑PL͒, PL excitation, and intra-and inter-band photocurrent spectroscopy. The influence of AlGaAs layers inserted into the QDIP active regions on the performance of dark current and inter-and intra-band photocurrent was examined. Initial results on intra-band responsivity and detectivity of these QDIPs at 77 K with undoped active region show promise for application.