Back-illuminated heterojunction photodiode

A back-illuminated heterojunction photodiode comprising:

• a substrate;
• a AIN layer formed above said substrate;
• a first AlGaN layer formed above said AIN layer;
• a second AlGaN layer formed above said first AlGaN layer;
• and
• a third AlGaN layer formed above said second AlGaN layer;
• wherein the Al fraction in the second AlGaN layer is less than the Al fraction in the first and third AlGaN layers.

A UV back-illuminated heterojunction photodiode comprising:

• a substrate transparent to at least a portion of a desired light spectrum, the desired light spectrum having wavelengths below about 360 nm;
• a first layer situated near said substrate, electrically conductive and at least substantially transparent to the portion of the light spectrum;
• a second layer situated next to said first layer and significantly absorptive to the portion of the desired light spectrum;
• and
• a third layer situated next to said second layer and electrically conductive.

A back-illuminated heterojunction photodiode having a backside and a frontside for detecting an incoming light beam, comprising:

• a substrate adjacent the backside of the photodiode, the substrate being substantially transparent to at least a portion of a desired light spectrum of the incoming light beam, the desired light spectrum having wavelengths below about 360 nm;
• an absorption layer positioned between the substrate and the frontside of the photo-diode, the absorption layer being significantly absorptive to the portion of the desired light spectrum;
• and
• the portion of the back-illuminated photodiode that extends from the substrate to the absorption layer is substantially transparent to the portion of the desired light spectrum.