Tuneable laser with improved suppression of auger recombination
A junction region for the laser diode may be improved to give an increased wavelength tuning range with improved thermal stability. The region has a homojunction structure that modifies the band structure to approximate that found in a type II superlattice. Up to half of the InGaAsP layer that nearest the p-InP region is n-type doped leaving the remainder with the original doping profile. This creates separate potential wells for electrons and holes in different parts of the InGaAsP layer. Also the barrier for electrons, but not for the holes, on the (p-InP)-(I-InGaAsP)-heterojunction may be increased by inserting a blocking layer of InAlAs, which is lattice matched to InP and InGaAsP, on the p-side between the above two materials.
1 . A tuneable laser having a timing section comprising a homojunction structure that modifies the band structure to approximate that found in a type IT superlattice.
2 . A tuneable laser having a tuning section comprising a homojunction structure comprising p and i layers, wherein up to half of the i layer is doped leaving the remainder with the original intrinsic state, so as to create separate potential wells for electrons and holes in different parts of the i layer.
3 . The tuneable laser as claimed claim 2 , wherein the region of the i layer nearest the p layer region is n-type doped, leaving the remainder undoped, to create a potential well for electrons in the n doped region of the i layer and a potential well for holes in the undoped region of this layer.
4 . A tuneable laser having a tuning section comprises p and i layers, wherein the region of the i layer nearest the p layer is n˜type doped, with the remainder of the region being p-doped, so as to create separate potential wells for electrons and holes in different parts of the i layers.
5 . The tuneable laser according to claim 2 , wherein the p layer is of InP.
6 . The tuneable laser according to claim 2 , wherein the i layer is InGaAsP.
7 . The tuneable laser according to claim 2 , wherein the homojunction structure modifies the band structure to approximate that found in a type n superlattice.
8 . A tuneable laser having a tuning section including a heterojunction comprising a blocking layer between the two materials thereof on the p-side, so as to increase the barrier for the electrons only, but not for the holes, while maintaining the same injection level for the electron and hole current.
9 . The tuneable laser as claimed in claim 8 , wherein insertion of the blocking layer provides an additional barrier for the electrons of about 0.2 eV and substantially no additional barrier for the holes.
10 . The tuneable laser as claimed in claim 8 , wherein the heterojunction is a (p-InP)-(i-InGaAsP)-structure > and the material of the blocking layer is lattice matched thereto.
11 . The tuneable laser as claimed in claim 10 , wherein the blocking layer comprises InAlAs.
12 . The tuneable laser as claimed in claim 10 , wherein the blocking layer comprises InAlAsR
13 . The tuneable laser as claimed in claim 8 , further comprising two delta-doped layers, one on each side of and adjacent to a central junction,
14 . (cancelled)