Recent advances in the research work on III-nitride semiconductors and Al/sub x/Ga/sub 1-x/N materials in particular has renewed the interest and led to significant progress in the development of ultraviolet (UV) photodetectors able to detect light in the mid- and near-UV spectral region (/spl lambda//spl sim/200-400 nm). There have been a growing number of applications which require the use of such sensors and, in many of these, it is important to be able to sense UV light without detecting infrared or visible light, especially from the Sun, in order to minimize the chances of false detection or high background. The research work on short-wavelength UV detectors has, therefore, been recently focused on realizing short-wavelength "solar-blind" detectors which, by definition, are insensitive to photons with wavelengths longer than /spl sim/285 nm. In this paper the development of Al/sub x/Ga/sub 1-x/N-based solar-blind UV detectors will be reviewed. The technological issues pertaining to material synthesis and device fabrication will be discussed. The current state-of-the-art and future prospects for these detectors will be reviewed and discussed.

Short-wavelength solar-blind detectors-status, prospects, and markets

III nitrides have become the most exciting challenge in optoelectronic materials in the last decade. Their intrinsic properties and an intense technological effort have made possible the fabrication of reliable and versatile detectors for short wavelengths. In this work, materials and devices issues are considered to provide a full picture of the advances in nitride UV photodetection. First, basic structures like photoconductors, Schottky, p-i-n and metal-semiconductor-metal photodiodes and phototransistors are compared, with emphasis on their specific properties and performance limitations. The efforts in the design and fabrication of more advanced detectors, in the search for higher quantum efficiency, contrast, signal-to-noise or speed operation, are reviewed afterwards. Metal-insulator-semiconductor diodes, avalanche photodetectors and GaN array detectors for UV imaging are also described. Further device optimization is linked with present materials issues, mainly due to the nitride quality, which is a direct result of the substrate used. The influence of substrates and dislocations on detector behaviour is discussed in detail. As an example of AlGaN photodetector applications, monitoring of the solar UV-B radiation to prevent erythema and skin cancer is presented.

https://iopscience.iop.org/article/10.1088/0953-8984/13/32/316/pdf

III nitrides and UV detection

GaN based modulation doped field effect transistors (MODFETs) and ultraviolet detectors are critically reviewed. AlGaN/GaN MODFETs with CW power levels of about 6 W (in devices with 1 mm gate periphery) and a minimum noise figure of 0.85 dB with an associated gain of 11 dB have been obtained at 10 GHz. As a precursor to solar-blind detectors that will be operative around 280 nm, where the solar radiation is absorbed by the ozone layer surrounding the earth, detector arrays with pixel sizes of 32×32 operative near the solar-blind region have been achieved. One does not have to rely on imagination to predict that devices with much improved performance will continue to be developed.

GaN-based modulation doped FETs and UV detectors

Self-assembled InGaN islands were grown by molecular-beam epitaxy on GaN, following a Stranski–Krastanow growth mode. Atomic force microscopy revealed that their dimensions were small enough to expect zero-dimensional quantum effects: the islands were typically 27 nm wide and 2.9 nm high. Strong blue-violet photoluminescence of the dots is observed, persisting up to room temperature. The temperature dependence of the photoluminescence is analyzed and compared to that of InGaN quantum well and bulk samples.

Self-assembled InGaN quantum dots grown by molecular-beam epitaxy

Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 μm. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results.

/pdf/time-resolved-photoluminescence-of-the-size-controlled-zno-3ty1tw61z3.pdf

Time-resolved photoluminescence of the size-controlled ZnO nanorods

A visible-blind UV camera based on a 32 × 32 array of backside-illuminated GaN/AlGaN p-i-n photodiodes has been successfully demonstrated. Each of the 1024 photodiodes in the array consists of a base n-type layer of AlGaN (~20%) onto which an undoped GaN layer followed by a p-type GaN layer is deposited by metallorganic vapor phase epitaxy. Double-side polished sapphire wafers are used as transparent substrates. Standard photolithographic, etching, and metallization procedures were employed to obtain fully-processed devices. The photodiode array was hybridized to a silicon readout integrated circuit using In bump bonds. Output from the UV camera was recorded at room temperature at a frame rate of 30 Hz. This new type of visible-blind digital camera is sensitive to radiation from 320 nm to 365 nm in the UV spectral region.

https://link.springer.com/content/pdf/10.1557/S109257830000065X.pdf

Visible-Blind UV Digital Camera Based On a 32 × 32 Array of GaN/AlGaN p-i-n Photodiodes

An ultraviolet-specific (320-365 nm) digital camera based on a 128×128 array of backside-illuminated GaN/AlGaN p-i-n photodiodes has been successfully developed. The diode structure consists of a base n-type layer of AlGaN (~23% Al) followed by undoped and then p-type GaN layers deposited by metal organic vapor phase epitaxy. Double-side polished sapphire wafers serve as transparent substrates. Standard photolithographic, etching, and metallization procedures were employed to fabricate the devices. The fully-processed photodiode array was hybridized to a silicon readout integrated circuit (ROIC) using In bump bonds for electrical contact. The UV camera was operated at room temperature at frame rates ranging from 15 to 240 Hz. A variety of UV scenes were successfully recorded with this configuration.

/pdf/uv-specific-320-365-nm-digital-camera-based-on-a-128-128-4n0bgcscox.pdf

UV-Specific (320-365 nm) Digital Camera Based On a 128×128 Focal Plane Array of GaN/AlGaN p-i-n Photodiodes

Visible-blind UV cameras based on a 32 × 32 array of backside-illuminated GaN/AlGaN p-i-n photodiodes have been successfully demonstrated. The photodiode arrays were hybridized to silicon readout integrated circuits (ROICs) using In bump bonds. Output from the UV cameras were recorded at room temperature at frame rates of 30–240 Hz. These new visible-blind digital cameras are sensitive to radiation from 285–365 nm in the UV spectral region.

High-Sensitivity Visible-Blind AlGaN Photodiodes and Photodiode Arrays

Visible-blind UV cameras based on a 32 × 32 array of backside-illuminated GaN/AlGaN p-i-n photodiodes have been successfully demonstrated. The photodiode arrays were hybridized to silicon readout integrated circuits (ROICs) using In bump bonds. Output from the UV cameras were recorded at room temperature at frame rates of 30−240 Hz. These new visible-blind digital cameras are sensitive to radiation from 285−365 nm in the UV spectral region.

/pdf/high-sensitivity-visible-blind-algan-photodiodes-and-26uajjwfnz.pdf

J. Boney

Papers

Visible-Blind UV Digital Camera Based On a 32 × 32 Array of GaN/AlGaN p-i-n Photodiodes

UV-Specific (320-365 nm) Digital Camera Based On a 128×128 Focal Plane Array of GaN/AlGaN p-i-n Photodiodes

High-Sensitivity Visible-Blind AlGaN Photodiodes and Photodiode Arrays

High-Sensitivity Visible-Blind AlGaN Photodiodes and Photodiode Arrays