The current density and dark current of a commercial photodetector were compared with those of our UV sensor (see Fig. 3). An order-of-magnitude increase was observed in the current density of our device in the UV region (200 to 350 nm) compared to the commercial Si photodetector. Therefore, a notable improvement in the efficiency (responsivity) of the SRO detector in the UV region was observed (the responsivity for the commercial UV-enhanced diode was obtained from a curve provided by the vendor).
The results clearly indicated that in the UV region the SRO-based UV detector presents a better response than the commercial one. It is necessary, however, to take into account that the numerical estimation of the responsivity (which exceeds unity in places) is obtained by comparing it with that of the commercial diode.
Two effects could produce the high responsivity observed. First, high responsivity can result from a very efficient shift from the UV to a longer, more easily detectable wavelength; therefore, the entire amount of UV-incident light could have contributed to the SRO emission. Furthermore, it is probable that light is emitted in the entire SRO film and all this light contributes to the diode photocurrent. Second, it has been observed in other studies that when SRO layers are used to produce voltage-induced p-n junctions as light detectors, high photocurrents are obtained even when the active area is covered by opaque aluminum.4 Thus, it is possible that SRO contributes in some other way to the diode photocurrent, so that an extra contribution to the responsivity has to be considered.
Many potential applications exist for sensitive UV detectors. For example, current and future optical digital storage will exploit blue and UV lasers (like Blu-ray and HD-DVD). Ultraviolet lasers emitting down to 250 nm can further increase optical-storage density; sensitive detectors will be needed for these systems.5
In the automotive industry, applications include inspecting muffler pipes for the presence of copper, detecting the presence of UV-curable gaskets, confirming the alignment of caps on connecting rods, and detecting the presence of lubricant on bearings. In packaging, UV light is used to detect the seal on ring-tab cans that prevents the seam from rusting, and is also used to detect glue on packages. In furniture manufacture, UV light helps detect the presence of excess glue in wood joints of furniture, is used to inspect the lumber for the proper coating of fungicide, and aids in controlling saws that cut wood marked with UV crayon. Other industrial uses include pharmaceutical and water treatment.
An important application of UV light is in water sterilization and food disinfection, in which it kills microorganisms. Ultraviolet technology is also suitable for use in flame detectors, fire alarms, and detection of invisible discharge phenomena such as corona discharge of high-voltage transmission lines. In addition, uses exist in health care (UV exposure measurements) and astronomy.
We are continuing to characterize the SRO-based UV sensor and improve its structure to further increase its UV sensitivity, and developing integrated structures. The Instituto Nacional de Astrofísica Óptica y Electrónica is a research institute with limited silicon-processing facilities; we are looking for a commercial producer interested in transferring this technology to the marketplace.❏
The authors wish to thank Pablo Alarcon for the sample preparation and Jacobo Ramos, Guadalupe Flores, Ignacio Juarez, and Juan Garcia for their technical support during the optical and electrical characterization. Finally, we appreciate the support from Lic. José Miguel Fernández Peña, and CONACyT, CECYT- Puebla (FOMIX).
1. D. Berman, M. Aceves, L. R. Berriel et. al., Phys. Stat. Sol. (c) 1(1) S1 (2004).
2. B. B. Jayant, Power Semiconductor Devices, PWS Publishing Co., Chap. 3 and 4 (1995).
3. D.W. Dong, E.A. Irene, and D.R. Young, J. Electrochem. Soc. 125(5) 819 (1978.
4. Z. Yu and M. Aceves-Mijares, Thin Solid Films 473(1) 145 (2004).
5. A. Ghazi et al., IEEE Trans. on Electron Devices 49(7) 1124 (2002).
DAINET BERMAN-MENDOZA, MARIANO ACEVE-MIJARES, LUIS RAÚL BERRIEL-VALDOS, JAZMÍN CARRANZA, and JORGE PEDRAZA are at Instituto Nacional de Astrofísica Óptica y Electrónica, Apdo. 51, Puebla, Puebla, 72000, Mexico; CARLOS DOMÍNGUEZ-HORNA is at IMB-CNM (CSIC) Campus UAB, 08913 Bellaterra, Spain; and CIRO FALCONY is at CINVESTAV, Depto. Física, Apdo. 17-740, México D.F., Mexico 07000; e-mails: daiber90@yahoo.com.mx, maceves@ieee.org, and berval@inaoep.mx.
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