Method and apparatus for a photodetector responsive over a selectable wavelength range
Photodetectors are constructed with ternary semiconductor alloys, for which the band gap varies with composition, to fabricate a photodetector and optical filter combination. The detectors are part of a measuring system that measures, stores and displays UV intensity versus time, peak intensity, total UV energy and temperature. It simultaneously measures a plurality of different UV ranges and temperatures. The output of the sensing system is converted to digital form and displayed on a visually perceptible device. Preferably total UV dosage and peak intensity are displayed for each monitored UV band, together with the maximum temperature. By manufacturing the photodetectors and filters with a ternary semiconductor alloy, sensors can be constructed which have a photoresponse to light in a narrow wavelength band and are blind to light outside of the wavelength band. Each sensor includes a filter and photodetector section, each of which includes ternary semiconductor alloys (i.e., both the filter and photodetector are fabricated at least in part with ternary semiconductor alloys).
1 . An ultraviolet light sensor, comprising:
a. a long pass filter;
b. a photodetector, wherein the photo-response range of the photodetector is at or below a wavelength of interest; and
c. wherein the first and second devices include AlGaN devices.
2 . The sensor of claim 1 , wherein the long pass filter and the photodetector have different band gaps adjusted by varying the Al and Ga concentrations in the ternary semiconductor Al x Ga 1-x N.
3 . The sensor of claim 2 , wherein Al is replaced with In.
4 . The sensor of claim 3 , further comprising a sapphire base to support the photodetector.
5 . The sensor of claim 4 , wherein a first side of the photodetector is placed directly on the sapphire base.
6 . The sensor of claim 5 , wherein the long pass filter is placed on the second side of the photodetector.
7 . The sensor of claim 6 , wherein the long pass filter is placed directly on the second side of the photodetector and the ternary semiconductor film filter includes a polycrystalline film with many internal light scattering surfaces.
8 . The sensor of claim 6 , wherein the long pass filter is on a transparent substrate and the ternary semiconductor film filter includes a polycrystalline film with many internal light scattering surfaces.
9 . The sensor of claim 1 , wherein the photodetector generates UV intensity signals comprised of electrical signals in response to incident UV light.
10 . The sensor of claim 9 , further comprising a data logger for storing the UV intensity signals and wherein the generated electrical signals are proportional to the incident UV light intensity.
11 . A UV light sensing system, comprising:
a) a housing;
b) a plurality of UV photodetectors located in the housing, at least two of the UV photodetectors tuned to different UV wavelengths, the UV photodetectors having a photo-response range at or below a wavelength of interest and fabricated from a ternary semiconductor; and
c) a plurality of corresponding long pass filters fabricated from a ternary semiconductor.
12 . The sensing system of claim 11 , wherein the plurality of long pass filters and corresponding photodetectors have different band gaps adjusted by varying the composition of the ternary semiconductor.
13 . The sensing system of claim 12 , wherein the ternary semiconductor is AlGaN or InGaN.
14 . The sensing system of claim 13 , wherein each of the plurality of photodetectors generate UV intensity signals based on the detected UV light.
15 . The sensing system of claim 14 , further comprising a data logger for storing the UV intensity signals.
16 . A method of detecting ultraviolet light, comprising:
a. directing ultraviolet light onto a transparent long pass filter constructed from Al y Ga 1-y N, wherein when the ultraviolet light is incident on the filter, then light below a first wavelength is absorbed;
b. directing the non-absorbed light onto a photodetector device constructed from Al x Ga 1-x N, wherein the ultraviolet light below a second wavelength is absorbed and the photodetector generates electrical signals corresponding to the intensity of the absorbed light.
17 . The method of claim 16 , further comprising adjusting the band gaps of the long pass filter and the photodetector by adjusting the Al and Ga concentrations of the AlGaN.
18 . The method of claim 17 , wherein the ternary semiconductor is InGaN.
19 . The method of claim 18 , further comprising storing the generated signals.