Light-emitting diode having a surface electrode of a tree-like form

• US 5,309,001 A
• Filed: 11/24/1992
• Issued: 05/03/1994
• Est. Priority Date: 11/25/1991
• Status: Expired due to Term

• Current Assignee: Schneider Electric SE
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Matsumoto, Mitsuhiro, Watanabe, Masanori, Sasaki, Kazuaki, Nakatsu, Hiroshi, Yamamoto, Osamu, Takeoka, Tadashi
• Primary Examiner(s): Hille, Rolf
• Assistant Examiner(s): TRAN, MINH LOAN
• Application Number:
  US07/980,666
• Time in Patent Office: 525 Days
• Field of Search: 257/13, 257/91, 257/94, 257/96, 257/773, 257/99
• US Class Current: 257/99
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/24 of the light emitting region, e.g. non-planar junction
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/385 the electrode extending at least partially onto a side surface of the semiconductor body

Abstract

A surface electrode on a surface of a LED has a pad, and further, at least first-order branches linearly extending from the pad, second-order branches diverged and linearly extending from the first-order branches, and third-order branches diverged and linearly extending from the second-order branches. The pad out of the surface electrode is not in electrical contact with a underlying semiconductor layer, whereas the surface electrode and the semiconductor layer are in electrical contact with each other at ends of the highest-order branches. Also, the semiconductor layer is provided along a pattern of the surface electrode in a mesa shape. Thus, ineffective light emission underneath the surface electrode is relatively reduced so that external quantum efficiency can be improved, and moreover even shorter-wavelength light can be allowed to go out at high efficiency by omitting a current diffusion layer.

Claims

1. A light-emitting diode comprising a semiconductor region, the semiconductor region including a light-emitting layer, stacked on a surface of a semiconductor substrate and a surface electrode stacked on the semiconductor region, and which further has a rear-face electrode on a rear face of the substrate, light emitted from the light-emitting layer being made to go out through a portion of the semiconductor layer that is not covered with the surface electrode, the surface electrode comprising at least:

a pad;

first-order branches linearly extending from the pad;

a plurality of second-order branches diverged and linearly extending from each of the first-order branches; and

a plurality of mth-order branches diverged and linearly extending from each (m-1)th-order branch, wherein m is a natural number greater than 2, each mth-order branch having a tip;

wherein no branch intersects any branch of lower or equal order except the branch from which it diverges and wherein the tips of the highest order branches do not intersect any other branch, the highest order being a natural number greater than 2.

2. A light-emitting diode as claimed in claim 1, wherein a line width of the branches of each order decreases as the number of order increases.

3. A light-emitting diode as claimed in claim 2, wherein a length of the branches of each order decreases at a constant rate as the number of order increases.

4. A light-emitting diode as claimed in claim 1, wherein a length of the branches of each order decreases at a constant rate as the number of order increases.

5. A light-emitting diode as claimed in claim 1, wherein an angle formed by adjoining lower- and higher-order branches is 0°

or 90°

.

6. A light-emitting diode as claimed in claim 1, wherein ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the pad of the surface electrode and the semiconductor region are electrically isolated from each other.

7. A light-emitting diode as claimed in claim 6, wherein the semiconductor region has, on a surface electrode side, a contact layer made of a material that makes ohmic contact with the surface electrode and having a conductive type of either p-type or n-type, and moreover has, between the contact layer and portions of the surface electrode other than the ends of the highest-order branches of the surface electrode, a current blocking layer having a conductive type different from that of the contact layer.

8. A light-emitting diode as claimed in claim 6, wherein a line width of the branches of each order decreases as the number of order increases.

9. A light-emitting diode as claimed in claim 1, wherein at least part of the semiconductor region is provided along a pattern of the surface electrode in a protruding mesa shape.

10. A light-emitting diode as claimed in claim 9, wherein the ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the rest of the surface electrode and the semiconductor region are electrically isolated from each there.

11. A light-emitting diode as claimed in claim 1, further comprising protrusions formed by at least part of the semiconductor region and provided under each end of the highest-order branches of the surface electrode.

12. A light-emitting diode as claimed in claim 11, wherein the ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the rest of the surface electrode and the semiconductor region are electrically isolated from each there.

13. A light-emitting diode as claimed in claim 1 wherein the number of higher-order branches extending from the tip of each branch is equal for each order of branches.

14. A light-emitting diode comprising a semiconductor region, the semiconductor region including a light-emitting layer, stacked on a surface of a semiconductor substrate and a surface electrode stacked on the semiconductor region, and which further has a rear-face electrode on a rear face of a substrate, light emitted from the light-emitting layer being made to go out through a portion of the semiconductor layer that is not covered with the surface electrode, the surface electrode comprising at least:

a pad;

first-order branches linearly extending from the pad;

second-order branches diverged and linearly extending from the first-order branches; and

third-order branches diverged and linearly extending from the second-order branches;

wherein ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the pad of the surface electrode and the semiconductor region are electrically isolated from each other; and

wherein the semiconductor region has, on a surface electrode side, a contact layer made of a material that makes ohmic contact with the surface electrode, and an insulating layer is provided between portions of the surface electrode other than the ends of the highest-order branches of the surface electrode, and the semiconductor region.

15. A light-emitting diode comprising a semiconductor region, the semiconductor region including a light-emitting layer, stacked on a surface of a semiconductor substrate and a surface electrode stacked on the semiconductor region, and which further has a rear-face electrode on a rear face of a substrate, light emitted from the light-emitting layer being made to go out through a portion of the semiconductor layer that is not covered with the surface electrode, the surface electrode comprising at least:

a pad;

first-order branches linearly extending from the pad;

second-order branches diverged and linearly extending from the first-order branches; and

third-order branches diverged and linearly extending from the second-order branches;

wherein ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the pad of the surface electrode and the semiconductor region are electrically isolated from each other; and

wherein the semiconductor region has, on a surface electrode side, a layer made of a material that yields a Schottky barrier with respect to the surface electrode, and moreover has, between the layer and the ends of the highest-order branches of the surface electrode, a contact layer made of a material that makes ohmic contact with the surface electrode.

16. A light-emitting diode comprising a semiconductor region, the semiconductor region including a light-emitting layer, stacked on a surface of a semiconductor substrate and a surface electrode stacked on the semiconductor region, and which further has a rear-face electrode on a rear face of a substrate, light emitted from the light-emitting layer being made to go out through a portion of the semiconductor layer that is not covered with the surface electrode, the surface electrode comprising at least:

a pad;

first-order branches linearly extending from the pad;

second-order branches diverged and linearly extending from the first-order branches; and

third-order branches diverged and linearly extending from the second-order branches;

wherein ends of the highest-order branches of the surface electrode and the semiconductor region are in electrical contact with each other while the pad of the surface electrode and the semiconductor region are electrically isolated from each other; and

wherein the surface electrode comprises an upper electrode provided on the entire region occupied by the surface electrode and made of a material that does not make ohmic contact with a surface of the semiconductor region, and a lower electrode provided between the upper electrode d and the surface of the semiconductor region at the ends of the highest-order branches and made of a material that makes ohmic contact with the semiconductor region surface.