# US 2014/0153603 A1 · Quantum cascade laser element

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- Number: US 2014/0153603 A1
- Document ID: US20140153603A1
- Status: Published application
- Kind: A1
- Application number: 14/236,458
- Filed: 2012-08-01
- Published: 2014-06-05
- Earliest claimed: 2011-08-02
- Assignees: Riken
- Inventors: Hideki Hirayama; Tsung-Tse Lin
- Web page: https://patentgrep.com/patent/US20140153603A1

## CPC

- H01S 5/3401: {having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers}
- B82Y 20/00: Nanooptics, e.g. quantum optics or photonic crystals
- H01S 5/3402: {intersubband lasers, e.g. transitions within the conduction or valence bands}
- H01S 5/0014: {Measuring characteristics or properties thereof (measuring techniques per se G01J, G01K, G01N, G01R)}
- H01S 5/0035: {Simulations of laser characteristics}
- H01S 5/0215: {Bonding to the substrate}
- H01S 5/0217: {Removal of the substrate}
- H01S 2302/02: THz - lasers, i.e. lasers with emission in the wavelength range of typically 0.1 mm to 1 mm
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES

## Abstract

[PROBLEM] To manufacture a quantum cascade laser (QCL) element having a reduced threshold current density (Jth) and an increased maximum operating temperature (Tmax). [SOLUTION] One embodiment of the present invention provides a THz-QCL element (1000) with a QCL structure (100), which is a semiconductor superlattice (100A) sandwiched between a pair of electrodes (20, 30). The semiconductor superlattice (100A) (QCL structure (100)) is provided with an active region (10) 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 (10) has repeating unit structures (10U) of a thickness, which includes sets of a well layer (10W) and a barrier layer (10B) alternatingly laminated with each other, wherein the well layer (10W) is made of AlxGa1-xAs (where 0<x<1), which is a mixed crystal of AlAs and GaAs.

## Claims

### Claim 1

A quantum cascade laser (QCL) element comprising a pair of electrodes and a semiconductor superlattice sandwiched by the pair of electrodes,
wherein the semiconductor superlattice has an active region that emits electromagnetic waves of THz range when an voltage is applied between the pair of electrodes,
wherein the active region has repeating unit structures, each unit structure having a thickness and including sets of a well layer and a barrier layer alternatingly laminated with each other, and wherein the well layer is made of AlxGa1-xAs (where 0<x<1), which is a mixed crystal of AlAs and GaAs.

### Claim 2 (depends on 1)

The QCL element according to claim 1,
wherein materials of the semiconductor superlattice are configured to satisfy, when an voltage for emission of the electromagnetic waves is applied,
ELO>kB T+E32,
where the ELO denotes energy of a longitudinal optical phonon that can be excited within the semiconductor superlattice, the E32 denotes a difference value between minimum energy E3 of the upper lasing level and minimum energy E2 of a lower lasing level, the T denotes operating temperature (unit:K), and the kB denotes Boltzmann constant.

### Claim 3 (depends on 2)

The QCL element according to claim 2,
wherein the materials of the semiconductor superlattice are configured to satisfy, when an voltage for emission of the electromagnetic waves is applied,
ELO>kB Telectron+E32,
where the Telectron denotes electron temperature (unit:K),
whereby non-radiative transition probability for electrons is reduced, the non-radiative transition is transition with which electrons thermally excited in the upper lasing level make transition from the upper lasing level to the lower lasing level mediated by electron-phonon scattering with the longitudinal optical phonons.

### Claim 4 (depends on 2, 3)

The QCL element according to claim 2 or 3,
wherein the semiconductor superlattice is configured to satisfy, when the voltage is applied,
ELO≦E21,
where the E21 denotes a difference value between the minimum energy E2 of the lower lasing level and minimum energy E1 of a depopulation level.

### Claim 5 (depends on 1)

The QCL element according to claim 1,
wherein the energy ELO of longitudinal optical phonons that can be excited in the interior of the semiconductor superlattice is greater than energy of longitudinal optical phonons that would be excited on the assumption that the well layer of the semiconductor superlattice were made of GaAs.

### Claim 6 (depends on 1)

The QCL element according to claim 1,
wherein the semiconductor superlattice has a energy barrier layer made of AlAs.