Maximizing electrical doping while reducing material cracking in III-V nitride semiconductor devices

• US 5,729,029 A
• Filed: 09/06/1996
• Issued: 03/17/1998
• Est. Priority Date: 09/06/1996
• Status: Expired due to Term

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Rudaz, Serge L.
• Primary Examiner(s): Jackson, Jerome
• Assistant Examiner(s): Kelley, Nathan K.
• Application Number:
  US08/709,355
• Time in Patent Office: 557 Days
• Field of Search: 257/13, 257/190, 257/191, 257/103, 257/183
• US Class Current: 257/13
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/325 characterised by the doping materials
• CPC Class Codes: H01S 5/305 characterised by the doping materials used in the laser structure
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/32341 blue laser based on GaN or GaP

Abstract

N-type doping in III-V-nitride semiconductor compounds, i.e. GaN-based compounds such as GaN, AlGaN, AlInN, InGaN, or AlGaInN, can be optimized to improve N-contact electrical resistance, carrier injection, forward voltage, and recombination characteristics without inducing cracking of the device layers. The N-type layer is constructed of sub-layers such that an N-type sub-layer is provided for each desired characteristic or property. The thickness of each sub-layer is carefully selected to avoid material cracking: the higher the required doping, the smaller the corresponding thickness. In illustration, the buffer layer of a light emitting device (LED) has three sub-layers. The first sub-layer is lightly doped to avoid cracking and is grown to the desired thickness for good material quality. The second sub-layer is heavily doped to provide good N-contact and electrical resistivity characteristics and is kept correspondingly as thin as necessary to avoid material cracking. The third sub-layer is doped to the desired level to provide optimum carrier injection and pair recombination in the active layer of the device.

Claims

1. A device comprising:

a substrate;

a compound device layer of (Al_x Ga_1-x)_y In_1-y N, positioned over the substrate, including a first and second sub-layer, wherein each sub-layer has an associated composition, thickness, and doping level; and

an active layer, positioned over the compound device layer;

wherein the composition and thickness associated with each of the sub-layers is adjusted to minimize material cracking, for each sub-layer the doping level is inversely proportional to the thickness.

2. A device, as defined in claim 1, further comprising:

a buffer layer interposing the substrate and the compound device layer.

3. A device, as defined in claim 2, the compound device layer further including a third sub-layer, having an associated doping and thickness, positioned over the second sub-layer, wherein the associated doping of the second and third sub-layers are independently adjusted, the doping of the second sub-layer is adjusted to minimize the electrical resistivity and forward voltage of the device under operation and the doping of the third sub-layer is adjusted to maximize the power output of the device.

4. A device, as defined in claim 1, wherein the associated doping level and thickness of the first sub-layer are further adjusted to minimize material dislocation and defect densities and the associated doping level of the second sub-layer is adjusted to minimize the electrical resistivity and device forward voltage.

5. A device, as defined in claim 4, wherein the associated doping level of the second sub-layer exceeds the associated doping level of the first sub-layer.

6. A device, as defined in claim 5, wherein the doping level changes continuously throughout the first and the second sub-layers.

7. A device, as defined in claim 6, wherein the composition changes continuously throughout the first and the second sub-layers.

8. A device, as defined in claim 5, wherein the composition changes continuously throughout from the first the second sub-layers.

9. A device, as defined in claim 5, wherein the ratio of the associated doping level of the first sub-layer to the associated doping level of the second sub-layer is between 1 and 100000.

10. A device, as defined in claim 4, the compound device layer further including a third sub-layer, having an associated doping and thickness, positioned over the second sub-layer, wherein the associated doping of the second and third sub-layers are independently adjusted, the doping of the second sub-layer is adjusted to minimize the electrical resistivity and forward voltage of the device under operation and the doping of the third sub-layer is adjusted to maximize the power output of the device.

11. A device, as defined in claim 1, wherein the compound device layer consists of P-type (Al_x Ga_1-x)_y In_1-y N material.

12. A device, as defined in claim 1, wherein the compound device layer consists of N-type (Al_x Ga_1-x)_y In_1-y N material.

13. A device, as defined in claim 12, wherein the associated doping level and thickness of the first sub-layer are further adjusted to minimize material dislocation and defect densities and the associated doping level of the second sub-layer is adjusted to minimize the electrical resistivity and device forward voltage.

14. A device, as defined in claim 13, wherein the associated doping level of the second sub-layer exceeds the associated doping level of the first sub-layer.

15. A device, as defined in claim 14, wherein the doping level changes continuously throughout the first and the second sub-layers.

16. A device, as defined in claim 14, wherein the composition changes continuously throughout the first and the second sub-layers.

17. A device, as defined in claim 14, wherein the ratio of the associated doping level of the first sub-layer to the associated doping level of the second sub-layer is between 1 and 10000.

18. A device, as defined in claim 13, the compound device layer further including a third sub-layer, having an associated doping and thickness., positioned over the second sub-layer, wherein the associated doping of the second and third sub-layers are independently adjusted, the doping of the second sub-layer is adjusted to minimize the electrical resistivity and forward voltage of the device under operation and the doping of the third sub-layer is adjusted to maximize the power output of the device.

19. A device, as defined in claim 18, wherein the associated doping level of the second sub-layer exceeds the associated doping level of the first sub-layer.

20. A device, as defined in claim 19, further comprising:

a buffer layer interposing the substrate and the compound device layer.

21. A device, as defined in claim 20, wherein the ratio of the associated doping level of the first sub-layer to the associated doping level of the second sub-layer is between 1 and 10000.