Spectrum detector

Abstract

A spectrum detector includes a substrate, a photodetector formed on the substrate and including a semiconductor having a plurality of convex portions, and a wavelength detection circuit for detecting a wavelength of light transmitted through the plurality of convex portions. Each photodetector comprises different convex portions different from one another with respect to at least one of size, pitch, and height. The photodetectors have a relationship expressed by formula L·m=λ·cos θ/(2 n ), wherein L is a diameter of each convex portion, n is a refractive index between the air and each convex portion of the GaN layer, m is an integer or a reciprocal of an integer, λ is a wavelength of light transmitted through the plurality of convex portions of each photodetector, and θ is an incident angle of the light with respect to a surface of the p-GaN layer.

What is claimed is: 
     
         1 . A spectrum detector, comprising:
 a substrate;   photodetectors arranged on the substrate, photodetectors comprising a semiconductor having a plurality of convex portions; and   a wavelength detection circuit configured to detect a wavelength of light transmitted through the plurality of convex portions,   wherein each photodetector comprises different convex portions different from one another with respect to at least one of size, pitch, and height, and wherein the wavelength detection circuit is configured to detect a wavelength of light transmitted through the plurality of convex portions of each photodetector,   wherein the photodetectors have a relationship expressed by formula (1),
     L·m =λ·cos θ/(2 n )  (1)
 
   wherein L is a diameter of each convex portion, n is a refractive index between the air and each convex portion of the GaN layer, m is an integer or a reciprocal of an integer, λ is a wavelength of light transmitted through the plurality of convex portions of each photodetector, and θ is an incident angle of the light with respect to a surface of the p-GaN layer.   
     
     
         2 . The spectrum detector of  claim 1 , wherein the plurality of photodetectors are configured to output optical voltages in response to incident light, and the wavelength detection circuit comprises:
 an optical voltage measurement circuit configured to measure the optical voltages respectively outputted from the plurality of photodetectors and to output an optical voltage measurement signal;   a memory configured to record a plurality of reference optical voltage measurement results and a plurality of reference potential difference results respectively corresponding to the plurality of photodetectors;   a waveform extraction circuit configured to extract a waveform of a comparison object from the optical voltage measurement signal and a reference optical voltage measurement signal;   a potential difference calculation circuit configured to calculate a potential difference of the waveform and to output a measurement potential difference; and   a comparison circuit configured to compare the measurement potential difference with the plurality of reference potential difference results and to detect a peak wavelength included in the incident light.   
     
     
         3 . The spectrum detector of  claim 2 , wherein the optical voltage measurement circuit is configured to measure an optical voltage outputted from each of the photodetectors when reference light including a known peak wavelength is incident on the plurality of photodetectors, and is configured to output a reference optical voltage measurement signal, and
 wherein the wavelength detection circuit comprises a control circuit configured to record the plurality of reference optical voltage measurement signals outputted from the optical voltage measurement circuit as the reference optical voltage measurement results in the memory.   
     
     
         4 . The spectrum detector of  claim 2 , wherein the potential difference calculation circuit is configured to calculate voltage differences of the plurality of reference optical voltage measurement results recorded in the memory and is configured to output the voltage differences as the reference potential difference results, and the control circuit is configured to record the plurality of reference potential difference results outputted from the potential difference calculation circuit in the memory. 
     
     
         5 . The spectrum detector of  claim 1 , wherein the plurality of photodetectors and the wavelength detection circuit are mounted on the same circuit board. 
     
     
         6 . The spectrum detector of  claim 1 , wherein the photodetector semiconductor comprises a GaN-based compound semiconductor. 
     
     
         7 . The spectrum detector of  claim 6 , wherein the GaN-based semiconductor is doped with an n-type material having a carrier concentration of less than 5×10 17  cm 3 . 
     
     
         8 . The spectrum detector of  claim 1 , wherein the photodetector comprises an n-type schottky photodetector comprising an n-type material having a carrier concentration of less than 5×10 17  cm 3 ; or, an I-layer. 
     
     
         9 . The spectrum detector of  claim 8 , wherein the I-layer comprises a layer in which there is no carrier, an undoped layer, or a p-type layer that has an n-type dopant.