Interband quantum well cascade laser, with a blocking quantum well for improved quantum efficiency

An interband quantum well cascade laser, comprising:

• a plurality of gain regions connected in series to form a stack, each gain region comprising:
• (a) an open-gap emitter region of semiconductor material having a lowest conduction subband and a highest valence subband, wherein a minimum energy of said lowest conduction subband and a maximum energy of said highest valence subband are spaced apart by an energy band-gap;
• (b) an open-gap collector region of semiconductor material having a lowest conduction subband and a highest valence subband;
• (c) an active region disposed between said emitter region and said collector region, said active region selected from the group consisting of:
• (i) a type-II heterojunction region, said type-II heterojunction region comprising:
• (A) an open-gap first quantum well region of semiconductor material, having a lowest conduction subband and a highest valence subband, wherein under a bias voltage the minimum energy of said lowest conduction subband of said first quantum well region is lower than the minimum energy of said lowest conduction subband of said emitter region;
• and
• (B) an open-gap second quantum well region of semiconductor material, disposed between said first quantum well region and said collector region, having a lowest conduction subband and a highest valence subband, wherein under said bias voltage said maximum energy of said highest valence subband of said second quantum well region is lower than the minimum energy of said lowest conduction subband of said first quantum well region and is higher than the maximum energy of said highest valence band of said first quantum well region;and
• (ii) a type-I region, said type-I region comprising:
• (A) an open-gap quantum well region of semiconductor material, having a lowest conduction subband and a highest valence subband, wherein under a bias voltage, the minimum energy of said lowest conduction subband of said type-I region being lower than the minimum energy of said lowest conduction subband of said emitter region;
• and
• (d) an open-gap blocking quantum well region of semiconductor material for preventing tunnelling or scattering leakage of electrons in conduction subbands of said active region to conduction subbands in said collector region, disposed between said active region and said collector region, having a lowest conduction subband and a highest valence subband, wherein under said bias voltage, the maximum energy of said highest valence subband of said blocking quantum well region being lower than the minimum energy of said lowest conduction subband of either said first quantum well region in the case where said active region is said type-II heterojunction region, or said type-I region in the case where said active region is said type-I region, and the minimum energy of said lowest conduction subband of said blocking quantum well region being higher than the minimum energy of said lowest conduction subband of either said first quantum well region in the case where said active region is said type-II heterojunction region, or said type-I region in the case where said active region is said type-I region, and said maximum energy of said highest valence subband of said blocking quantum well being higher than the minimum energy of said lowest conduction subband of said collector region;
• further comprising a second barrier region of semiconductor material, disposed between said active region and said blocking quantum well region, said second tunnel barrier region adapted for confining said hole wave function to said active region, thereby increasing said overlap between said electron wave function and said hole wave function in said active region, and further adapted for blocking electrons in said active region from tunnelling or scattering into said collector region;
• and
• further comprising a third barrier region of semiconductor material, disposed between said blocking quantum well region and said collector region, said third tunnel barrier region adapted for blocking electrons in said active region from tunnelling or scattering into said collector region and for reducing internal absorption losses due to interband transitions between said valence subbands in said blocking quantum well region and said conduction subbands in said collector region;
• cladding layers at opposing ends of said stack;
• and
• a voltage source, for applying a bias to said stack;
• said stack disposed in an optical cavity.

An interband quantum well laser, comprising:

• a gain region comprising:
• (a) an open-gap emitter region of semiconductor material having a lowest conduction subband and a highest valence subband, wherein a minimum energy of said lowest conduction subband and a maximum energy of said highest valence subband are spaced apart by an energy band-gap;
• (b) an open-gap collector region of semiconductor material having a lowest conduction subband and a highest valence subband;
• (c) an active region disposed between said emitter region and said collector region, said active region selected from the group consisting of:
• (i) a type-II heterojunction region, said type-II heterojunction region comprising:
• (A) an open-gap first quantum well region of semiconductor material, having a lowest conduction subband and a highest valence subband, wherein under a bias voltage the minimum energy of said lowest conduction subband of said first quantum well region is lower than the minimum energy of said lowest conduction subband of said emitter region;and
• (B) an open-gap second quantum well region of semiconductor material, disposed between said first quantum well region and said collector region, having a lowest conduction subband and a highest valence subband, wherein under said bias voltage said maximum energy of said highest valence subband of said second quantum well region is lower than the minimum energy of said lowest conduction subband of said first quantum well region and is higher than the maximum energy of said highest valence band of said first quantum well region;and
• (ii) a type-I region, said type-I region comprising:
• (A) an open-gap quantum well region of semiconductor material, having a lowest conduction subband and a highest valence subband, wherein under a bias voltage, the minimum energy of said lowest conduction subband of said type-I region being lower than the minimum energy of said lowest conduction subband of said emitter region;
• and
• (d) an open-gap blocking quantum well region of semiconductor material for preventing tunnelling or scattering leakage of electrons in conduction subbands of said active region to conduction subbands in said collector region, disposed between said active region and said collector region, having a lowest conduction subband and a highest valence subband, wherein under said bias voltage, the maximum energy of said highest valence subband of said blocking quantum well region being lower than the minimum energy of said lowest conduction subband of either said first quantum well region in the case where said active region is said type-II heterojunction region, or said type-I region in the case where said active region is said type-I region, and the minimum energy of said lowest conduction subband of said blocking quantum well region being higher than the minimum energy of said lowest conduction subband of either said first quantum well region in the case where said active region is said type-II heterojunction region, or said type-I region in the case where said active region is said type-I region, and said maximum energy of said highest valence subband of said blocking quantum well being higher than the minimum energy of said lowest conduction subband of said collector region;
• further comprising a second barrier region of semiconductor material, disposed between said active region and said blocking quantum well region, said second tunnel barrier region adapted for confining said hole wave function to said active region, thereby increasing said overlap between said electron wave function and said hole wave function in said active region, and further adapted for blocking electrons in said active region from tunnelling or scattering into said collector region;
• and
• further comprising a third barrier region of semiconductor material, disposed between said blocking quantum well region and said collector region, said third tunnel barrier region adapted for blocking electrons in said active region from tunnelling or scattering into said collector region and for reducing internal absorption losses due to interband transitions between said valence subbands in said blocking quantum well region and said conduction subbands in said collector region;
• cladding layers at opposing ends of said gain region;
• and
• a voltage source, for applying a bias to said gain region;
• said stack disposed in an optical cavity.