Optical semiconductor device

Claim 2

An optical semiconductor device which is capable of emitting light when an active region of the device is energised, the device including, in the active region, a first region of band gap energy substantially lower than that of the material immediately adjacent to the first region, a first control port for energising the active region, a second region, and a second control port for energising the second region of the semiconductor device, which second region is capable of influencing the light emitted by the device, characterised in that, the second region of the semiconductor device includes a further region of band gap energy substantially lower than that of the material immediately adjacent to the further region.

Claim 3

An optical semiconductor device as claimed in claim 1, wherein the further region is located in the active region.

Claim 4

An optical semiconductor device as claimed in claim 2, wherein the active region of the semiconductor device includes a PNP structure, or an NPN structure, and the first and further regions are located in the respective junctions of the PNP or NPN structure.

Claim 5

An optical semiconductor device as claimed in claim 1, wherein the semiconductor device has a substantially PNP structure, or a substantially NPN structure, one PN junction lies within the active region and accommodates the first region, and the other PN junction lies in a light-guiding region and accommodates the further region.

Claim 6

An optical semiconductor device as claimed in any one of the preceding claims, wherein the further region has a multiple quantum well structure.

Claim 7

An optical semiconductor device as claimed in claim 5, wherein the first region has a multiple quantum well structure.

Claim 8

An optical semiconductor device as claimed in any one of the preceding claims, which is a laser which is tunable by current injected into the second control port.

Claim 9

An optical semiconductor device as claimed in any one of claims 1 to 6, which is an optical amplifier, the gain of which is controllable by current injected into the second control port.

Claim 10

An optical semiconductor device as claimed in any one of claims 1 to 6, which is an optical switch which is switchable by current injected into the second control port.

Claim 11

A communication system including an optical semicon­ductor device as claimed in any one of the preceding claims.

Claim 12

A semiconductor laser having a first pn structure including two semiconductor layers of different conductivity, and an active layer of a band gap energy narrower than that of two semiconductor layers formed therebetween, which is characterized in that a second pn structure is formed within the same optical waveguide structure on one side of said two semiconductor layers to form a pnp structure or an npn structure with said first pn structure, and a layer with a band gap energy narrower than that of the semiconductor layers of both sides thereof on a pn junction of said pn structure.

Claim 13

A semiconductor laser having a first pn structure including two semiconductor layers of different conductivity, and an active layer of a band gap energy narrower than that of two semiconductor layers formed therebetween, which is characterized in that a second pn structure is formed within the same optical waveguide structure on one side of said two semiconductor layers to form a pnp structure or an npn structure with said first pn structure, and a layer with a band gap energy narrower than that of the semiconductor layers of both sides thereof on a pn junction of said pn structure.

Claim 14

A semiconductor laser of either the pnp structure or the npn structure including two layers of a narrower band gap energy than the adjacent layer one of which is formed as an active layer, a separation semiconductor layer provided between said two layers, two outer semiconductor layers sandwiching said two layers and having conductivity different from said separation semiconductor layer, and a buried layer of the same conductivity as said separation semiconductor which buries at least said separation semi­conductor layer, which is characterized in that a high resistance layer is provided between said buried layer and at least one of said two outer semiconductor layers.

Claim 15

A semiconductor laser of either the pnp structure or the npn structure including two layers of a narrower band gap energy than the adjacent layer one of which is formed as an active layer, a separation semiconductor layer provided between said two layers, two outer semiconductor layers sandwiching said two layers and having conductivity different from said separation semiconductor layer, and a buried layer of the same conductivity as said separation semiconductor which buries at least said separation semi­conductor layer, which is characterized in that a high resistance layer is provided between said buried layer and at least one of said two outer semiconductor layers.

Claim 16

A semiconductor laser as claimed in Claim 12, wherein said high resistance layer includes a pn junction of reverse bias.

Claim 17

A semiconductor light emitting device including two semiconductor layers of different conductivity, and a third semiconductor layer formed between said two semiconductor layers which has a narrower band gap energy than the two semiconductor layers, which is characterized in that a fourth semiconductor layer is provided between at least one of said two semiconductor layers and said third semi­conductor layer to have a band gap energy still narrower than that of said third semiconductor layer.

Claim 18

A semiconductor light emitting device including two semiconductor layers of different conductivity, and a third semiconductor layer formed between said two semiconductor layers which has a narrower band gap energy than the two semiconductor layers, which is characterized in that a fourth semiconductor layer is provided between at least one of said two semiconductor layers and said third semi­conductor layer to have a band gap energy still narrower than that of said third semiconductor layer.

Claim 19

A semiconductor light emitting device having a first pn structure including two semiconductor layers of different conductivity and a first active layer formed between said two semiconductor layers with a band gap energy narrower than that of said two semiconductor layers, which is characterized in that a second pn structure is provided within the same optical waveguide structure on one side of said two semiconductor layers to form with said first pn structure either a pnp structure or an npn structure, and a second active layer is formed on the pn junction of said second pn structure having a band gap energy narrower than those of semiconductors on both sides thereof and different from that of said first active layer.

Claim 20

A semiconductor light emitting device having a first pn structure including two semiconductor layers of different conductivity and a first active layer formed between said two semiconductor layers with a band gap energy narrower than that of said two semiconductor layers, which is characterized in that a second pn structure is provided within the same optical waveguide structure on one side of said two semiconductor layers to form with said first pn structure either a pnp structure or an npn structure, and a second active layer is formed on the pn junction of said second pn structure having a band gap energy narrower than those of semiconductors on both sides thereof and different from that of said first active layer.