Riken Corporation

Tsung-Tse Lin

Hideki Hirayama

Miho Sasaki

Li Wang

Ke Wang

To increase the maximum operating temperature of quantum cascade lasers of a terahertz region, a quantum cascade laser elementaccording to the present invention has a semiconductor superlattice structure sandwiched between a pair of electrodes, the semiconductor superlattice structure has an active regionthat emits electromagnetic waves of a frequency in a THz region under an external voltage applied through the pair of electrodes for operation, and the active regionhas plural unit structuresU, each of which is repeatedly layered over one another. Each of the unit structuresU has a double quantum well structure formed of a first well layerWand a second well layerWseparated from each other by a barrier layer, the first well layerWand the second well layerWhave compositions different from each other, and when the external voltage is not being applied, potential energy for electrons in the second well layerWis lower than that in the first well layerW

Quantum cascade laser element

[PROBLEM] To manufacture a quantum cascade laser (QCL) element having a reduced threshold current density (J) and an increased maximum operating temperature (T). [SOLUTION] One embodiment of the present invention provides a THz-QCL element () with a QCL structure (), which is a semiconductor superlattice (A) sandwiched between a pair of electrodes (). The semiconductor superlattice (A) (QCL structure ()) is provided with an active region () that emits THz range electromagnetic waves due to the transition of electrons between sub-bands during application of a voltage to the pair of electrodes, for example. The active region () has repeating unit structures (U) of a thickness, which includes sets of a well layer (W) and a barrier layer (B) alternatingly laminated with each other, wherein the well layer (W) is made of AlGaAs (where 0&#x3c;x&#x3c;1), which is a mixed crystal of AlAs and GaAs.

To raise the upper limit of the temperature range in which a quantum cascade laser (QCL) element for THz range operates at a single frequency. In a quantum cascade laser element in one embodiment of the present invention, each unit structureU in the active regionis provided with the first to fourth well layersW-Wthat are stacked in this order and separated from one another by at least one bather layerB. During application of a first bias electric field for lasing, the structure of electronic energy levels has a reception, upper lasing, lower lasing, and depopulation levels and emits electromagnetic waves at a first frequency. During application of a second bias electric field that is weaker than the first bias electric field, the overlap integral is 0.15 or less between electronic wavefunctions for the unnecessary upper lasing and unnecessary lower lasing levels, thereby stimulated emissions of electromagnetic waves are suppressed at frequencies other than the first frequency.

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Wako, Japan

Tsung-Tse Lin