Electrically switching transverse modes in high power THz quantum cascade lasers.

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions

Temperature dependence of gas-detection sensitivity of InGaAsSb/AlGaAsSb DFB lasers

The detection sensitivity of <0.50 ppb-m of HF gas is achieved with CW GaSb-based DFB lasers at 2396 nm. Sensitivity was characterized over laser operating temperature and output power. \ua9 2011 OSA.Peer reviewed: YesNRC publication: Ye

Continuous-wave operation of type-I GaSb-based narrow ridge waveguide lasers near 3254nm

Narrow ridge waveguide (5um) laser diodes were fabricated using type-I InGaAsSb/AlInGaAsSb quantum well active regions on GaSb. The devices operate in continuous-wave mode near 3254nm with a total light output of 7.4mW at 20\ub0C (uncoated facets). \ua9 2012 OSA.Peer reviewed: YesNRC publication: Ye

NIR, MWIR and LWIR quantum well infrared photodetector using interband and intersubband transitions

The article of record as published may be located at http://dx.doi.org/10.1016/j.infrared.2006.10.021This paper presents the design, fabrication and characterization of a QWIP photodetector capable of detecting simultaneously infrared radiation within near infrared (NIR), mid wavelength infrared (MWIR) and long wavelength infrared (LWIR). The NIR detection was achieved using interband transition while MWIR and LWIR were based on intersubband transition in the conduction band. The quantum well structure was designed using a computational tool developed to solve self-consistently the Schro¨dinger–Poisson equation with the help of the shooting method. Intersubband absorption in the sample was measured for the MWIR and LWIR using Fourier transform spectroscopy (FTIR) and the measured peak positions were found at 5.3 lm and 8.7 lm which agree well with the theoretical values obtained 5.0 lm and 9.0 lm for the two infrared bands which indicates the accuracy of the self-consistent model. The photodetectors were fabricated using a standard photolithography process with exposed middle contacts to allow separate bias and readout of signals from the three wavelength bands. The measured photoresponse gave three peaks at 0.84 lm, 5.0 lm and 8.5 lm wavelengths with approximately 0.5 A/W, 0.03 A/W and 0.13 A/W peak responsivities for NIR, MWIR and LWIR bands, respectively. This work demonstrates the possibility of detection of widely separated wavelength bands using interband and intersubband transitions in quantum wells.The work is supported in part by a grant through the Research Office of the Naval Postgraduate School

Temperature dependence of gas-detection sensitivity of InGaAsSb/AlGaAsSb distributed feedback lasers at 2396\u2005nm

The HF gas detection sensitivity of GaSb-based distributed feedback lasers was studied in order to evaluate the potential use of operating temperature to control the laser output power in field applications. Measurements were made in the 2f wavelength modulation spectroscopy mode to monitor a prominent HF absorption feature at 2396\u2005nm. An Allan variance analysis indicates that the best sensitivity is obtained when a larger thermoelectric current is applied to maintain temperature control by actively heating or cooling the laser. The reduced detection sensitivity for a setpoint near the ambient laser operating temperature is similar to that obtained without active temperature control.Peer reviewed: YesNRC publication: Ye

Lateral diffusion of titanium disilicide as a route to contacting hybrid Si/organic nanostructures

We characterized microscopic patterns of TiSi2 using atomic force microscopy and scanning tunneling microscopy, to test the possibility of using silicide contacts for experiments on the nanoscopic scale. We observed the effect on the morphology of incomplete formation of the disilicide, and studied the growth of lateral extension due to atomic diffusion. Upon diffusion, the silicide forms a neat and clean interface some hundreds of nanometers from the bulk electrode. That spreading phenomenon is our central focus, as we believe it may be useful in future efforts to make narrowly spaced contacts.NRC publication: Ye

High-resolution methane spectroscopy using InGaAsSb/AlInGaAsSb laterally-coupled index-grating distributed feedback laser diode at 3.23 \u3bcm

A lateral etched-grating process was used to produce singlemode distributed feedback laser diodes at 3.23 \u3bcm. The devices are based on InGaAsSb/AlInGaAsSb type-I quantum well active regions grown on GaSb substrates by molecular beam epitaxy. The lasers were used in high-resolution spectroscopy of methane gas near the v3, R7 vibrational absorption transitions.Peer reviewed: YesNRC publication: Ye

LWIR/SWIR Switchable Two Color Device based on InP/InGaAs Integrated HBT/QWIP

NRC publication: Ye

Dual spectral InGaAs/InP quantum well infrared photodetector focal plane array

NRC publication: Ye

Single-mode mid-infrared lasers for gas sensing in the 2-4um range

Type-I interband laser diodes were developed for trace gas sensing applications in the 2-4um wavelength range. The devices were grown by molecular beam epitaxy on GaSb substrates using InGaAsSb/Al(In)GaAsSb active regions. Tunable, single-mode lasers were produced using distributed feedback grating processing or by incorporating Fabry-Perot lasers in an external cavity configuration. Sensitive gas detection was demonstrated using these lasers in tunable-diode laser absorption spectroscopy. \ua9 2011 IEEE.Peer reviewed: YesNRC publication: Ye