QWIP with enhanced optical coupling

• US 20040159775A1
• Filed: 02/18/2004
• Published: 08/19/2004
• Est. Priority Date: 12/24/1999
• Status: Active Grant

• Current Assignee: Mind Fusion, LLC (Ascend Innovation Management, LLC)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Sundaram, Mani, Reisinger, Axel R.
• Granted Patent: US 7,238,960 B2
• Time in Patent Office: Days
• US Class Current: 250/214.1
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 27/1462 Coatings
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/14647 Multicolour imagers having a stacked pixel-element structure, e.g. npn, npnpn or MQW elements
• CPC Class Codes: H01L 27/14667 Colour imagers
• CPC Class Codes: H01L 27/14689 MOS based technologies
• CPC Class Codes: H01L 31/02161 for devices characterised by at least one potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/02327 the optical elements being integrated or being directly associated to the device, e.g. back reflectors optical coatings H01L31/0216
• CPC Class Codes: H01L 31/03046 including ternary or quaternary compounds, e.g. GaAlAs, InGaAs, InGaAsP
• CPC Class Codes: H01L 31/035236 Superlattices; Multiple quantum well structures
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials

Abstract

A QWIP structure is disclosed that is configured with enhanced optical coupling to improve absorption capability and efficiency. A waffle-type light-coupling grating having a pattern of etched holes operates to improve absorption by preventing photons from bouncing out of the detector sensing areas. A post-type light coupling grating can also be used. Parameters of the grating, including its orientation, pitch, and etch depth, can be adjusted to optimize specific color detection. The grating can include a hybrid metal layer including both ohmic and reflective qualities to further improve quantum and conversion efficiency. A “photon-in-a-box” configuration is also disclosed, where sides of the QWIP sensing areas are coated with reflective metal to further inhibit the escaping of photons. The material design and number of quantum wells per QWIP can be selected so as to exploit the avalanche effect, thereby increasing device responsivity.

Claims

1. A pixel-registered photo detector array comprising:

one or more detector layers of semiconductor material, each detector layer between contact layers of semiconductor material, thereby defining a stack of layers having a front side and a back side; and

a waffle-type light-coupling grating formed on the backside of the stack, the grating having a pattern of holes that reflects a substantial portion of light coming into the array so as to disperse that light through the one or more detector layers, thereby facilitating absorption.

2. The array of claim 1 wherein the pattern of the waffle-type light-coupling grating has a geometry optimized for a center wavelength of interest, and an orientation ranging from about 20 to 70 degrees.

3. The array of claim 2 wherein the geometry includes a hole depth of about one quarter wavelength of the center wavelength of interest, and a spacing between the holes of about the center wavelength of interest.

4. The array of claim 2 wherein the orientation is about 45 degrees.

5. The array of claim 1 wherein the array has a plurality of detector layers, each having a different light absorption versus wavelength response curve thereby enabling a multicolor photo detector.

6. The array of claim 1 wherein edges of the one or more detector layers are reflectively coated so as to provide, in conjunction with the waffle-type light-coupling grating, a photon-in-a-box configuration for containing light within each pixel of the array.

7. The array of claim 1 wherein the waffle-type light-coupling grating includes a hybrid metal layer having both ohmic and reflective qualities.

8. The array of claim 1 wherein each of the one or more detector layers is about one micron or less in thickness.

9. The array of claim 1 wherein each of the contact layers is electrically coupled to a respective electrical contact on the backside, thereby facilitating hybridization where the array is connected to a substrate configured with supporting electrical circuitry.

10. The array of claim 1 wherein the array is configured as a strained-InGaAs/AlGaAs QWIP structure having a limited number of quantum wells so as to enable exploitation of avalanche effects.

11. A pixel-registered photo detector array comprising:

one or more detector layers of semiconductor material, each detector layer between contact layers of semiconductor material, thereby defining a stack of layers having a front side and a back side;

a light-coupling grating formed on the backside of the stack with a hybrid metal layer having both ohmic and reflective qualities, and having a pattern that reflects a substantial portion of light coming into the array so as to disperse that light through the one or more detector layers, thereby facilitating absorption;

wherein edges of the one or more detector layers are reflectively coated so as to provide, in conjunction with the light-coupling grating, a photon-in-a-box configuration for containing light within each pixel of the array.

12. The array of claim 11 wherein the pattern of the light-coupling grating is a waffle-type grating and has a geometry that includes a hole depth of about one quarter wavelength of a center wavelength of interest, and a spacing between the holes of about the center wavelength of interest.

13. The array of claim 11 wherein the pattern of the light-coupling grating has an orientation of about 45 degrees.

14. The array of claim 11 wherein the array has a plurality of detector layers, each having a different light absorption versus wavelength response curve thereby enabling a multicolor photo detector.

15. The array of claim 11 wherein each of the one or more detector layers is about one micron or less in thickness.

16. The array of claim 11 wherein each of the contact layers is electrically coupled to a respective electrical contact on the backside, thereby facilitating hybridization where the array is connected to a substrate configured with supporting electrical circuitry.

17. A pixel-registered photo detector array comprising:

one or more detector layers of semiconductor material, each detector layer between contact layers of semiconductor material, thereby defining a stack of layers of a multicolor photo detector having a front side and a back side;

a rotated light-coupling grating formed on the backside of the stack, the light-coupling grating having a pattern that reflects a substantial portion of light coming into the array so as to disperse that light through the one or more detector layers, thereby facilitating absorption.

18. The array of claim 18 wherein the rotated light-coupling grating has an orientation of about 45 degrees, and has one of a waffle-type or post-type pattern.

19. The array of claim 18 wherein the light-coupling grating includes a hybrid metal layer having both ohmic and reflective qualities, and edges of each detector layer are reflectively coated so as to provide, in conjunction with the light-coupling grating, a photon-in-a-box configuration for containing light within each pixel of the array.

20. The array of claim 18 wherein the array is configured as a strained-InGaAs/AlGaAs QWIP structure having a limited number of quantum wells so as to enable exploitation of avalanche effects.