Abstract: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-p… Show more
“…The incorporation of the different additives into the cellulose network altered mainly the characteristics of the films in the ultraviolet (UV) region (200–400 nm). An enhanced light transmittance of films in this region is of importance for some UV optoelectronic devices, such as light emitting diodes (LEDs) 20 and photodiodes 21 – 23 . Figure 4 Light transmittance of films made of: ( a ) TOCNF and PVA, ( b ) TOCNF and Gx, ( c ) TOCNF and AZC, ( d ) TOCNF, PVA and Gx, ( e ) TOCNF, PVA and AZC.…”
We systematically investigated the effect of film-forming polyvinyl alcohol and crosslinkers, glyoxal and ammonium zirconium carbonate, on the optical and surface properties of films produced from TEMPO-oxidized cellulose nanofibers (TOCNFs). In this regard, UV-light transmittance, surface roughness and wetting behavior of the films were assessed. Optimization was carried out as a function of film composition following the “random forest” machine learning algorithm for regression analysis. As a result, the design of tailor-made TOCNF-based films can be achieved with reduced experimental expenditure. We envision this approach to be useful in facilitating adoption of TOCNF for the design of emerging flexible electronics, and related platforms.
“…The incorporation of the different additives into the cellulose network altered mainly the characteristics of the films in the ultraviolet (UV) region (200–400 nm). An enhanced light transmittance of films in this region is of importance for some UV optoelectronic devices, such as light emitting diodes (LEDs) 20 and photodiodes 21 – 23 . Figure 4 Light transmittance of films made of: ( a ) TOCNF and PVA, ( b ) TOCNF and Gx, ( c ) TOCNF and AZC, ( d ) TOCNF, PVA and Gx, ( e ) TOCNF, PVA and AZC.…”
We systematically investigated the effect of film-forming polyvinyl alcohol and crosslinkers, glyoxal and ammonium zirconium carbonate, on the optical and surface properties of films produced from TEMPO-oxidized cellulose nanofibers (TOCNFs). In this regard, UV-light transmittance, surface roughness and wetting behavior of the films were assessed. Optimization was carried out as a function of film composition following the “random forest” machine learning algorithm for regression analysis. As a result, the design of tailor-made TOCNF-based films can be achieved with reduced experimental expenditure. We envision this approach to be useful in facilitating adoption of TOCNF for the design of emerging flexible electronics, and related platforms.
“…Despite these technical difficulties, several groups have achieved limited success in demonstrating visible and solar-blind focal plane array (FPA) cameras of various sizes. 4,5,6,7 In this paper we present the results of a 320 x 256 AlGaN based solar-blind focal plane array camera, and then discuss future improvements that could improve the imaging performance. We start by looking at the I-V and photoresponse characteristics of single 25 µm x 25 µm pixel AlGaN-based solar-blind photodetectors.…”
Back-illuminated solar-blind ultraviolet p-i-n photodetectors and focal plane arrays are investigated. We initially study single-pixel devices and then discuss the hybridization to a read-out integrated circuit to form focal plane arrays for solar-blind UV imaging. The photodetectors consist of an AlGaN p-i-n active region grown atop a high quality AlN template layer with a ~1 µm thick Al 0.5 Ga 0.5 N:Si-In co-doped low-resistance UV-transparent lateral conduction layer. The material is processed into a 320 x 256 array of 25 µm x 25 µm pixels using standard lithographic techniques. Typical pixels demonstrate a peak responsivity of 93 mA/W at 278 nm; this corresponds to an external quantum efficiency of 42%. The uniformity of the array is discussed, and a selection of sample images from the solarblind focal plane array is included. In addition, recent attempts to achieve shorter wavelength deep UV backilluminated p-i-n photodetector and focal plane arrays are also discussed.
“…Applications for UV imagers include biological agent detection, missile and shellfire detection, atmospheric ozone-level detection, welding imagery and flame sensing. Additionally, large-format UV staring FPAs based on GaN photodiodes may play an important role in obtaining UV images of the stars and other astronomical objects of importance for understanding the creation and evolution of the universe [3].…”
GaN detector arrays are hybridized to a Si readout integrated circuit (ROIC) using flip-chip bonding techniques. GaN is transparent for visible light. Then, visible light will be absorbed by the Si ROIC. It can affect the performance of the ROIC. In this paper, we discuss the mechanism of these effects: under visible light illumination, during the integration period, the photocurrents generated by the PMOS reset switch and NMOS test switch are accumulated by the integration capacitor, while during the readout period, the photocurrent generated by the PMOS sampling switch is accumulated by the sample/hold capacitor. These effects can be reduced by covering an extra aluminium layer on the top of the readout circuit, which is proved to be effective by experiment.
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