Terahertz Quantum Cascade Laser Operating at 2.94 THz

The development of quantum cascade laser at 2.94 THz is reported. The laser structure is based on a bound-to-continuum active region and a semi-insulating surface-plasmon waveguide. Lasing is observed up to a heat-sink temperature of 70 K in pulsed mode with light power of 4.75 mW at 10 K and 1 mW at 70 K. A threshold current density of 296.5 A/cm(2) and an internal quantum efficiency of 1.57 x 10(-2) per cascade period are also observed at 10 K. The characteristic temperature of this laser is extracted to be T-0 = 57.5 K.

Surface Emitting Distributed Feedback Quantum Cascade Laser around 8.3 mu m

We demonstrate surface emitting distributed feedback quantum cascade lasers emitting at wavelengths from 8.1 mu m at 90 K to 8.4 mu m at 210 K. The second-order metalized grating is carefully designed using a modified coupled-mode theory and fabricated by contact lithography. The devices show single mode behavior with a side mode suppression ratio above 18 dB at all working temperatures. At 90 K, the device emits an optical power of 101 mW from the surface and 199 mW from the edge. In addition, a double-lobe far-field pattern with a separation of 2.2 degrees is obtained in the direction along the waveguide.

Growth and characterization of InGaAs/InAlAs quantum cascade lasers

The growth and characterization of quantum cascade (QC) lasers based on InGaAs/InAlAs material system are investigated. Pronounced intersubband absorption from stacked active region of QC structure is used to monitor the wavelength of QC laser and disclose the material quality. The precise control of the epilayer thickness and the good quality of interfaces are demonstrated by the abundant narrow satellite peaks of X-ray diffraction. Laser action in quasi-continuous wave operation is achieved at lambda approximate to 5.1-5.2 mum up to 300 K. For 10 x 800 mum(2) laser device, peak output power of similar to7.2 mW and threshold current density of 3 kA/cm(2) at room temperature are obtained. For some devices, if keep the peak output powers at the similar to2 mW level, quasi-continuous wave operation at room temperature persists more than 1 h are recorded. (Q) (C) 2001 Elsevier Science Ltd. All rights reserved.

Investigation on InGaAs/InAlAs quantum cascade lasers

The preparation and main characteristics of the InGaAs/InAlAs quantum cascade laser were given. The device has a reinforced ridge waveguide structure. The threshold current obtained at 80K is about 0. 5A, and the corresponding threshold current density is about 5kA/cm(2).

Strain-compensated quantum cascade lasers operating at room temperature

Quantum cascade (QC) lasers based on strain-compensated InxGa(1-x)As/InyAl(1-y)As grown on InP substrate using molecular beam epitaxy is reported. The epitaxial quality is demonstrated by the abundant narrow satellite peaks of double-crystal X-ray diffraction and cross-section transmission electron microscopy of the QC laser wafer. Laser action in quasi-continuous wave operation is achieved at lambda approximate to 3.6-3.7 mum at room temperature (34 degreesC) for 20 mum x 1.6 mm devices, with peak output powers of similar to 10.6mW and threshold current density of 2.7kA/cm(2) at this temperature. (C) 2000 Published by Elsevier Science B.V.

Room temperature (34 degrees C) operation of strain-compensated quantum cascade lasers

A short wavelength (lambda similar or equal to 3.5 mu m) strain-compensated InxGa(1-x)As/InyAl(1-y)As quantum cascade laser is reported. Quasi-continuous wave operation of this device at 34 degrees C with an output power of 11.4mW persisted for more than 30 minutes without obvious degradation. A very low threshold current density of 1.2KA/cm(2) at this temperature was observed.

Small-divergence singlemode emitting tapered distributed-feedback quantum cascade lasers

A tapered distributed feedback quantum cascade laser emitting at lambda similar to 8.1 mu m is reported. Utilising a tapered waveguide structure with a surface metal grating, the device exhibited singlemode operation over the temperature range of 100 to 214 K, with sidemode suppression ratio > 20 dB and a nearly diffraction limited far-field beam divergence angle of 5.4 degrees.

Application of step-scan FTIR to the research of quantum cascade lasers

The principle of step-scan Fourier transform infrared （FTIR） spectroscopy is introduced. Double modulation step-scan FTIR technique is used to obtain the quantum cascade laser＇s stacked emission spectra in the time domain. Optical property and thermal accumulation of devices due to large drive current are analyzed.

Room Temperature Operation of Strain-Compensated 5.5μm Quantum Cascade Lasers

Room temperature operation is an important criterion for high performance of quantum cascade lasers. A strain-compensated quantum cascade laser（λ≈5.5μm） with optimized waveguide structure lasing at room temperature is reported. Accurate control of layer thickness and strain-compensated material composition is demonstrated using X-ray diffraction. An output power of at least 45mW per facet is realized for a 20μm-wide and 2mm-long laser at room temperature.

n-type Ge-SiGe quantum cascade structure utilizing quantum wells for electrons in the L and Gamma valleys

In this letter, we propose an n-type vertical transition bound-to-continuum Ge-SiGe quantum cascade structure utilizing electronic quantum wells in the L and F valleys of the Ge layers. The optical transition levels are located in the quantum wells in the L valley. Under a bias of 80 kV/cm, the carriers in the lower level are extracted by miniband transport and L - Gamma tunneling into the subband in the Gamma well of the next period. And then the electrons are injected into the upper level by ultrafast intervalley scattering, which not only effectively increases the tunneling rate and suppresses the thermal backfilling of electrons, but also enhances the injection efficiency of the upper level. The performance of the laser is discussed.

High-power operation of uncoated strain-compensated quantum cascade lasers at 4.8 mu m

High-power operation of uncoated 22-mu m-wide quantum cascade lasers (QCLs) emitting at lambda approximate to 4.8 mu m is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated In0.68Ga0.32As/In0.37Al0.63As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64kA/cm(2). The effects of varying the cavity lengths from 1 to 4mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm(-1) is extracted.

Solid source MBE growth of quantum cascade lasers

High material quality is the basis of quantum cascade lasers (QCLs). Here we report the solid source molecular beam epitaxy (MBE) growth details of realizing high quality of InGaAs/InAlAs QCL structures. Accurate control of material compositions, layer thickness, doping profile, and interface smoothness can be realized by optimizing the growth conditions. Double crystal x-ray diffraction discloses that our grown QCL structures possess excellent periodicity and sharp interfaces. High quality laser wafers are grown in a single epitaxial run. Room temperature continuous-wave (cw) operation of QCLs is demonstrated.

Low-threshold high-temperature operation of lambda similar to 7.4 mu m quantum cascade lasers

We report low-threshold high-temperature operation of 7.4 mu m strain-compensated InGaAs/InAlAs quantum cascade lasers (QCLs). For an uncoated 22-mu m-wide and 2-mm-long laser, the low-threshold current densities, i.e. 0.33 kA/cm(2) at 81 K in pulsed mode and 0.64 kA/cm(2) at 84 K in cw mode, are realized. High-temperature operation of uncoated devices, with a high value of 223 K, is achieved in cw mode.

High-power and low-threshold-current-density GaAs/AlGaAs quantum cascade lasers

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 mu m above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60 mu m respectively, a peak output power more than 500 mW is achieved in pulsed mode operation. A low threshold current density J(th) = 2.6 kA/cm(2) gives the devices good lasing characteristics. In a drive frequency of 1 kHz, the laser operates up to 20% duty cycle.

High-performance strain-compensated InGaAs/InAlAs quantum cascade lasers

We report on the realization of quantum cascade (QC) lasers based on strain-compensated InxGa(1-x)As/In(y)A((1-y))As grown on InP substrates using molecular beam epitaxy. X-ray diffraction and cross section transmission electron microscopy have been used to ascertain the quality of the QC laser materials. Quasi-continuous wave lasing at lambda approximate to 3.54-3.7 mum at room temperature was achieved. For a laser with 1.6 mm cavity length and 20 mum ridge-waveguide width,quasi-continuous wave lasing at 34 degreesC persists for more than 30 min, with a maximum power of 11.4 mW and threshold current density of 1.2 kA cm(-2), both record values for QC lasers of comparable wavelength.