LIGHT EMITTING ELEMENT, LIGHT EMITTING ELEMENT ARRAY, OPTICAL WRITING HEAD, AND IMAGE FORMING APPARATUS
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-unit thyristor including stacked semiconductor layers having a pnpn structure, and
a current confinement structure,
the current confinement structure including a high-resistance region and a conductive region, and confining carriers in the conductive region.
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, and
the current confinement structure is formed in a p-type anode layer in the light-emitting-unit thyristor.
4 . The light emitting element according to claim 2 , wherein
the current confinement structure is a semiconductor layer including p-type Al, and
the current confinement structure is formed in a p-type anode layer in the light-emitting-unit thyristor.
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-unit thyristor, and a gate which is also shared by the light-emitting-unit 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-unit 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 6 , 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-unit 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-unit 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 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 cathode layer of the light-emitting-unit 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 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 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 cathode layer of the light-emitting-unit 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-unit 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 .