Germanium on insulator for CMOS imagers in the short wave infrared
Light detecting structures comprising germanium (Ge) photodiodes formed in a device layer of a germanium on-insulator (GeOI) wafer, focal planes arrays based on such Ge photodiodes (PDs) and methods for fabricating such Ge photodiodes and focal plane arrays (FPAs). An FPA includes a Ge-on-GeOI PD array bonded to a ROIC where the handle layer of the GeOI layer is removed. The GeOI insulator properties and thickness can be designed to improve light coupling into the PDs.
1. A method for forming a light detecting structure, comprising:
a) providing a germanium-on-insulator (GeOI) wafer that includes a handle layer, a Ge device layer and an insulator layer between the handle layer and the Ge device layer, wherein the insulator layer is a quarter wave layer;
b) forming an array of Ge photodiodes in the Ge device layer;
c) coupling the array of Ge photodiodes mechanically and electrically to a read only integrated circuit; and
d) removing the handle layer to provide a focal plane array.
2. The method of claim 1 , wherein the insulator layer includes silicon oxide.
3. The method of claim 1 , wherein the insulator includes germanium oxide.
4. The method of claim 1 , wherein each Ge photodiode of the array of photodiodes is a vertical PN photodiode.
5. The method of claim 1 , wherein adjacent Ge photodiodes of the array of Ge photodiodes are electrically isolated from each other.
6. The method of claim 1 , wherein the focal plane array can detect light in the short wave infrared (SWIR) regime.
7. The method of claim 1 , wherein the quarter-wave layer is replaced by a quarter-wave stack.
8. A device, comprising:
a) an array of germanium (Ge) photodiodes formed in a Ge device layer of a germanium-on-insulator (GeOI) wafer, wherein a handle layer of the GeOI wafer is removed to leave an insulator layer of the GeOI wafer facing incoming light and wherein the insulator layer is a quarter wave layer; and
b) a silicon readout integrated circuit (ROIC) bonded to the Ge device layer, wherein the array of Ge photodiodes is coupled electrically to the ROIC to form a focal plane array for detecting the incoming light.
9. The device of claim 8 , wherein the insulator includes silicon oxide.
10. The device of claim 8 , wherein the insulator includes germanium oxide.
11. The device of claim 8 , wherein each Ge photodiode is a vertical PN photodiode.
12. The device of claim 8 , wherein adjacent Ge photodiodes of the array of Ge photodiodes are electrically isolated from each other.
13. The device of claim 8 , wherein the light is in the short wave infrared (SWIR) regime.
14. The device of claim 8 , wherein the quarter-wave layer is replaced by a quarter-wave stack.