Light emitting element, light emitting element array, optical writing head, and image forming apparatus
View Patent ↗A light emitting element includes a semiconductor substrate, and an island structure formed on the semiconductor substrate. The island structure includes a light-emitting-unit thyristor and a current confinement structure. The light-emitting-unit thyristor includes stacked semiconductor layers having a pnpn structure. The current confinement structure includes a high-resistance region and a conductive region, and confines carriers in the conductive region.
1. A light emitting element comprising:
a semiconductor substrate; and
an island structure formed on the semiconductor substrate,
the island structure including
a light-emitting thyristor including stacked semiconductor layers having a pnpn structure, the pnpn structure having an anode layer provided on the semiconductor substrate, a n-type gate layer provided on the anode layer, a p-type gate layer provided on the n-type gate layer, and a cathode layer provided on the p-type gate layer, and
a current confinement structure,
the current confinement structure being provided in the anode layer and including a high-resistance region and a conductive region, and confining carriers in the conductive region; and
wherein the anode layer comprises a first anode layer and a second anode layer, and the current confinement structure is provided between the first anode layer and the second anode layer, wherein the current confinement structure is provided directly below the first anode layer, and wherein the current confinement structure is provided directly above the second anode layer.
2. The light emitting element according to claim 1 , wherein the high-resistance region is an oxidation region that is formed by selectively oxidizing the current confinement structure from at least one side surface of the island structure.
3. The light emitting element according to claim 1 , wherein
the current confinement structure is a semiconductor layer including p-type Al.
4. The light emitting element according to claim 2 ,
wherein the current confinement structure is a semiconductor layer including p-type Al.
5. The light emitting element according to claim 1 , wherein
the current confinement structure is formed of p-type AlAs or AlGaAs, and
the high-resistance region is an oxidation region of AlAs or AlGaAs.
6. The light emitting element according to claim 1 , wherein
the island structure further includes a shifting-unit thyristor including the semiconductor layers having the pnpn structure on the semiconductor substrate, and
the shifting-unit thyristor has a top cathode layer which is separate from a top cathode layer of the light-emitting thyristor, and a gate which is also shared by the light-emitting thyristor.
7. The light emitting element according to claim 6 , wherein the conductive region of the current confinement structure is formed directly below the cathode layer of the shifting-unit thyristor.
8. The light emitting element according to claim 5 , wherein
the island structure further includes a diode and a parasitic thyristor immediately below the diode, the diode being formed by a top pn layer in the pnpn structure on the semiconductor substrate, the parasitic thyristor including the semiconductor layers having the pnpn structure on the semiconductor substrate,
the parasitic thyristor has a top cathode layer which is separate from the cathode layer of the light-emitting thyristor and the cathode layer of the shifting-unit thyristor, and
the high-resistance region of the current confinement structure is formed directly below the cathode layer of the parasitic thyristor.
9. The light emitting element according to claim 1 , wherein
the island structure further includes a diode and a parasitic thyristor immediately below the diode, the diode being formed by a top pn layer in the pnpn structure on the semiconductor substrate, the parasitic thyristor including the semiconductor layers having the pnpn structure on the semiconductor substrate,
the parasitic thyristor has a top cathode layer which is separate from the cathode layer of the light-emitting thyristor and the cathode layer of the shifting-unit thyristor, and
the high-resistance region of the current confinement structure is formed directly below the cathode layer of the parasitic thyristor.
10. The light emitting element according to claim 8 , wherein
the parasitic thyristor includes a diode formed by a pn junction with the top cathode layer of the parasitic thyristor,
the diode has an anode electrode formed on a p-type semiconductor layer, and a cathode electrode formed on the cathode layer, and
the anode electrode of the diode serves as a gate electrode which is shared by the light-emitting thyristor and the shifting-unit thyristor.
11. The light emitting element according to claim 8 , wherein
an area ratio of the high-resistance region in the current confinement structure to the cathode layer of the parasitic thyristor when the cathode layer overlaps the high-resistance region is larger than an area ratio of the high-resistance region in the current confinement structure to the top cathode layer of the shifting-unit thyristor when the cathode layer overlaps the high-resistance region, and is larger than an area ratio of the high-resistance region in the current confinement structure to the top cathode layer of the light-emitting thyristor when cathode layer overlaps the high-resistance region.
12. The light emitting element according to claim 9 , wherein
an area ratio of the high-resistance region in the current confinement structure to the top cathode layer of the parasitic thyristor when the cathode layer overlaps the high-resistance region is larger than an area ratio of the high-resistance region in the current confinement structure to the top cathode layer of the shifting-unit thyristor when the cathode layer overlaps the high-resistance region, and is larger than an area ratio of the high-resistance region in the current confinement structure to the top cathode layer of the light-emitting thyristor when cathode layer overlaps the high-resistance region.
13. The light emitting element according to claim 8 , wherein
the island structure further includes a groove formed adjacent to the cathode layer of the parasitic thyristor and extending parallel to the cathode layer of the parasitic thyristor,
the groove has a depth that reaches at least the current confinement structure, and
the current confinement structure is exposed on a side surface of the island structure by the groove, and is selectively oxidized from the side surface.
14. The light emitting element according to claim 13 , wherein
the island structure is divided into a first island structure and a second island structure by the groove, the first island structure having an anode electrode of the diode, the second island structure having a gate electrode which is shared by the light-emitting thyristor and the shifting-unit thyristor.
15. The light emitting element according to claim 8 , wherein
the high-resistance region is formed entirely directly below the cathode layer of the parasitic thyristor.
16. The light emitting element according to claim 9 , wherein
the high-resistance region is formed entirely directly below the cathode layer of the parasitic thyristor.
17. A self-scanning light emitting element array comprising:
a plurality of light emitting elements each being the light emitting element according to claim 8 , wherein
a first transfer signal is applied to the cathode layer of the shifting-unit thyristor of an island structure located at an odd-number position among the island structures in the plurality of light emitting elements, and a second transfer signal different from the first transfer signal is applied to the cathode layer of the shifting-unit thyristor of an island structure located at an even-number position among the island structures in the plurality of light emitting elements, and
the gates of the shifting-unit thyristors of adjacent island structures among the island structures in the plurality of light emitting elements are electrically connected to each other via the diodes.
18. An optical writing head comprising the light emitting element array according to claim 17 .
19. An image forming apparatus comprising the optical writing head according to claim 18 .
20. A light emitting element comprising:
a semiconductor substrate; and
an island structure formed on the semiconductor substrate,
the island structure including
a light-emitting thyristor including stacked semiconductor layers having a pnpn structure, the pnpn structure having an anode layer provided on the semiconductor substrate, a n-type gate layer provided on the anode layer, a p-type gate layer provided on the n-type gate layer, and a cathode layer provided on the p-type gate layer, and
a current confinement structure,
the current confinement structure being provided in the anode layer and including a high-resistance region and a conductive region, and confining carriers in the conductive region; and
wherein the anode layer comprises a first anode layer and a second anode layer, and the current confinement structure is provided between the first anode layer and the second anode layer, wherein the first anode layer has a bottom surface in direct contact with the current confinement structure, and wherein the second anode layer has a top surface in direct contact with the current confinement structure.