Monolithic array of light emitting diodes for the generation of light at multiple wavelengths and its use for multicolor display applications

• US 5,952,680 A
• Filed: 03/06/1997
• Issued: 09/14/1999
• Est. Priority Date: 10/11/1994
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Strite, Samuel C.
• Primary Examiner(s): Tran, Minh Loan
• Application Number:
  US08/809,162
• Time in Patent Office: 922 Days
• Field of Search: 257/87, 257/88, 257/89, 257/90, 257/101, 257/102, 257/103
• US Class Current: 257/88
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H01L 33/0033 having Schottky barriers
• CPC Class Codes: H01L 33/0037 having a MIS barrier layer
• CPC Class Codes: H01L 33/325 characterised by the doping materials

Abstract

An array of light emitting diodes (LEDs) for the generation of light at multiple wavelengths. The LEDs are realized in a layered structure of semiconductor films grown on one substrate, said array comprising conducting portions for applying a bias to said LEDs and insulating portions, wherein at least one of the insulating or conducting portions is formed by a lateral variation of doping conditions of the top layer of the structure.

Claims

1. A monolithic array of light emitting diodes (LEDs) for the generation of light at multiple wavelengths, comprising:

a substrate;

a layered structure of semiconductor films formed on the substrate including a top layer most distant from the substrate;

a plurality of LEDs formed in the layered structure, at least one LED being a metal-insulator-semiconductor (MIS) diode including an insulating portion and a conducting portion both formed in the top layer, wherein at least one of the insulating portion and the conducting portion is formed by a lateral variation of doping conditions of the top layer.

2. The array of claim 1, wherein at least one of the LEDs has an active region, and an electroluminescence spectrum determined by impurity states in the material forming the active region, said impurity states leading to optical transistions with energies below the bandgap energy of the active region.

3. The array of claim 2, wherein the electroluminescence spectrum of at least one of the LEDs comprises at least two different emission wavelengths, whereby a change in a bias applied to the LED causes a change in relative intensity of the electroluminescence at the emission wavelengths of the LED.

4. The array of claim 2, wherein the electroluminescence spectrum of at least one of the LEDs comprises only one emission line at one wavelength.

5. The array of claim 1, wherein the doping conditions are dependent on at least one of dopant type, local concentration, and doping process.

6. The array of claim 1, wherein light from the LEDs is partially radiated into at least one of a halfspace above the substrate, and a halfspace below the substrate.

7. The array of claim 1, wherein the substrate is transparent for generated light and part of the generated light is radiated through the substrate.

8. The array of claim 1, wherein more than one of the LEDs is based on a metal-insulator-semiconductor structure.

9. The array of claim 1, wherein at least one LED has its insulating portion embedded in its conducting portion.

10. The array of claim 1, wherein at least one LED has its conducting portion embedded in its insulating portion.

11. The array of claim 1, wherein at least one LED is a p-n junction based device having an active region, and dopants responsible for an emission wavelength associated with the LED are contained in the active region.

12. The array of claim 1, wherein the layered structure of semiconductor films is based on the material system (Ga_1-x Al_x)_1-y In_y N.

13. The array of claim 1, wherein contact areas for applying a bias to a particular LED are on the same side of the substrate.

14. The array of claim 1, wherein the substrate is conductive and serves as a common electrode of at least two LEDs.

15. The array of claim 1, wherein n different wavelengths, n greater than or equal to 2, are generated, and n times m LEDs are geometrically arranged in m equivalent pixels, m greater than or equal to 1, each pixel containing n adjacent subpixels, and each of the n subpixels being identified with one LED for the generation of one of the n different wavelengths.

16. The array of claim 15, wherein the material composition of the semiconductor films is chosen such that the fundamental absorption edge is in one of the blue spectral range or the ultraviolet spectral range, and the doping conditions in the active regions for the LEDs are chosen such that at least one subpixel serves for the generation of light in the spectral range between ultraviolet and bluegreen, at least one subpixel serves for the generation of light in the spectral range between bluegreen and yellow, and at least one subpixel serves for the generation of light in the spectral range between yellow and infrared.

17. The array of claim 16, wherein each pixel contains 3 subpixels and the pixels are arranged in a two-dimensional array.

18. A multicolor display comprising:

a layered structure of semiconductor films formed on the substrate including a top layer most distant from the substrate;

an LED array comprising a plurality of LEDs formed in the layered structure, at least one LED being a metal-insulator-semiconductor (MIS) diode including an insulating portion and a conducting portion both formed in the top layer, wherein at least one of the insulating portion and the conducting portion is formed by lateral variation of doping conditions of the top layer;

means for addressing and applying a bias to individual LEDs in said LED array; and

a mechanical mount for supporting said LED array such that individual light sources attributed to the LEDs can be viewed.

19. The multicolor display of claim 18, further comprising:

means for controlling the bias applied to the individual LEDs; and

an interface for receiving image data to be displayed.

20. The multicolor display of claim 19, wherein the means for controlling the bias applied to the individual LEDs also comprises a means for controlling the light intensity of the LEDs.

21. The multicolor display of claim 19, further comprising a timing system for handling time-dependent image data.

22. The multicolor display of claim 19, further comprising a gray scale processor for handling gray levels of individual subpixels.

23. The multicolor display of claim 19, further comprising a pulse generator for biasing the LEDs in a pulsed mode.

24. A multicolor projection display comprising:

a layered structure of semiconductor films formed on a substrate including a top layer most distant from the substrate;

an LED array comprising a plurality of LEDs formed in the layered structure, at least one LED being a metal-insulator-semiconductor (MIS) diode including an insulating portion and a conducting portion both formed in the top layer, wherein at least one of the insulating portion and the conducting portion is formed by lateral variation of doping conditions of the top layer;

means for addressing and applying a bias to individual LEDs in said LED array;

a mechanical mount for supporting said LED array such that individual light sources attributed to the LEDs can be viewed; and

an optical imaging system for a projection of the light sources of the multicolor display.

25. The multicolor projection display of claim 24, further comprising means for projection on a screen.

26. A computer including a multicolor display, the multicolor display comprising:

a layered structure of semiconductor films formed on a substrate including a top layer most distant from the substrate;

an LED array comprising a plurality of LEDs formed in the layered structure, at least one LED being a metal-insulator-semiconductor (MIS) diode including an insulating portion and a conducting portion both formed in the top layer, wherein at least one of the insulating portion and the conducting portion is formed by lateral variation of doping conditions of the top layer;

means for addressing and applying a bias to individual LEDs in said LED array; and

a mechanical mount for supporting said LED array such that individual light sources attributed to the LEDs can be viewed.