Far-infrared〜THz light emitter based on InAs/GaSb quantam cascade structures

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Far-infrared〜THz intersubband light emitters based on InAs/GaSb quantum cascade structures were investigated theoretically and experimentally. In order to realize high efficiency light emitter, intersubband electroluminescence was characterized by step-scan Fourier transform infrared spectrometer(FT-IR) and low-temperature cryostat.The summary of the research results are :1. Calculated threshold current density of type-II InAs/GaSb intersubband emitter showed that it was about one-fifth as small as that of type-I GaAs/AlGaAs and GaInAs/AlInAs systems.2. Intersubband electroluminescence from InAs/AlSb quantum cascade structures having large tunability of emission wavelength was observed for the first time.3. Temperature and structure dependence of intersubband electroluminescence was instigated by step-scan FT-IR and low-temperature cryostat. Calculated subband structures were found to be in close agreement with extperimental results.4. Optical properties of InAs/AlSb multi-quantum wells epitaxially grown on GaAs substrates with a buffer layer were shown to be dependent on the type of the interface bond and buffer layer material. X-ray diffraction measurements revealed that lattice matching between the average lattice constant of multi-quantum well and the buffer layer plays a key role in determining the optical properties.5. Carrier recycling in type-II InAs/GaSb quantum cascade structures was investigated. It has been observed that the emission power was proportional to the periods of cascade structures, which indicated that injected carriers were recycled in type-II cascade structures.6. The new type-II InAs/GaSb light emitting structures was proposed. Theoretical calculation showed that new structures could emit electro-magnetic waves in the THz region without going to an extreme design.