Dilute nitride type-II "W" structures have potential for lasing at 1.55 microns (on GaAs substrates) and in the mid-infrared (3-6 microns, on InP substrates). The former active regions utilize (In)GaAsN/GaAsSb/(In)GaAsN/GaAs quantum wells, whereas the latter are based on InAsN/GaAsSb/InAsN/GaInP structures. Following a review of the theoretical rationale, we will present some preliminary MOCVD growth results for the GaAs-based type-II structures, along with their characterization by x-ray, TEM, and photoluminescence. The experimental energy gaps corresponding to the layer compositions determined from characterization are in good agreement with calculations based on the 10-band k×p formalism.
Wide stripe and single-mode ridge guide dilute nitride quantum well lasers exhibit high performance in the 1.3 micron wavelength region. Optimizing the MOCVD growth of InGaAsN has yielded devices displaying reduced temperature sensitivity compared with conventional InP-based structures. Current annealing effects in InGaAsN QW lasers are minimized through the use of a nitrogen only cool down after growth of the laser structure. Device studies reveal the impact of nitrogen content and quantum well barrier materials on the optical gain, carrier confinement, and laser characteristics. Extension of the emission wavelength in MOCVD grown structures remains challenging. Higher N content results in a significant increase in threshold current density and higher temperature sensitivity.
High performance strained-layer InGaAs (λ=1.2μm) and InGaAsN (λ=1.3μm) quantum-well lasers have been realized by MOCVD growth using Arsine and Dimethylhydrazine as the group V precursors. The use of GaAsP high bandgap barrier layers is shown to improve device performance over conventional GaAs barrier lasers. By comparison to conventional InP-based technology, InGaAsN lasers exhibit very low threshold current density at high temperature (390A/cm2 at 80°C), using a single-quantum well design.
The presence of surface states, which pins the Fermi level within the bandgap, contributes to the degradation in the performance of light-emitting diodes (LEDs) and p-i-n photodiodes due to an increase in the non-radiative recombination rate. Chemical modification on the facet or device surface can greatly enhance the output power of LED's and photocurrent of p-i-n photodiodes. Adsorbing molecules can change either the density or energy distribution of surface states. This effect leads to changes in surface recombination which result in systematic variations in light output, and thus the effect can be used for detection of analytes. This mechanism was used to realize a compact chemical sensor based on III/V LED/Detector structures. Initially, we fabricated InGaAlP/InGaP/InGaAlP double heterostructure (DH) LEDs (400 X 1000 micrometer2) with three different active region thicknesses: 50, 250 and 500 nm. In constant current mode, the DH LED exhibits electroluminescence (EL) at approximately 670 nm for an InGaP active region. The EL intensity changes of the LED in various gaseous ambients (NH3, NH2(CH3), NH(CH3)2, N(CH3)3, and SO2) are measured. The data show reproducible trends: DH LED structures with thicker active regions result in larger emission intensity changes due to analyte adsorption. Our findings are consistent with active-layer surface area dependence. Thicker active layer devices have larger carrier losses due to nonradiative surface recombination, and thus show a stronger sensitivity to the surface chemistry. Furthermore, we used this DH LED design to build a highly versatile compact sensor. The MOCVD-grown LED wafer is patterned and chemically etched to fabricate integrated GaAs/AlGaAs edge-emitting LEDs and p-i-n photodiode units. The light emitted from the edge-emitting LEDs is absorbed at the sidewall of the adjacent photodiode, and the resulting photocurrent is measured. The device design concept is based on increasing the ratio of analyte-accessible facet area to the volume of the active region. This integrated LED- photodiode device can serve as an on-line chemical sensor for a variety of analytes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.