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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Photonic Crystal Surface Emitting GaSb-Based Type-I Quantum Well Diode Lasers

The GaSb-based epitaxially regrown monolithic diode PCSELs operating near 2 μm at room temperature in continuous wave regime and generating 30 mW of output power from 200 μm diameter aperture have been designed and fabricated. Here, the devices demonstrated CW threshold current density of about 500 A/cm 2 . The laser output power was enhanced thanks to increased buried void area fill-factor in the photonic crystal layer with multiple voids per unit cell. The PCSEL generated ultra-low divergence donut shape beams at the currents near threshold. At higher injection currents, the device brightness was limited by excitation of the higher order lateral modes. Generation of the vector-vortex beams of different types by different band edge states of the buried photonic crystal was observed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1985

Molecular beam epitaxial growth and transmission electron microscopy studies of thin GaAs/InAs(100) multiple quantum well structures

GaAs/InAs(100) multiple interface structures involving 7.4 percent lattice mismatch have been fabricated via molecular beam epitaxy and examined via transmission electron microscopy. It is found that high-quality, dislocation-free interfaces involving such high lattice mismatch can indeed be experimentally realized for very thin layers provided proper care is given to achieve a balance between the growth kinetics and the thermodynamics leading to the equilibrium ground state of the strained layer. The compressive strain is homogeneously accommodated and a tetragonal distortion is induced in the InAs layer with a perpendicular lattice constant in close agreement with that expected on the basis of the continuum theory and elastic constants of bulk InAs.

Grunthaner, F. J.↗
NASA NTRS1985

Structure variation of the index of refraction of GaAs-AlAs superlattices and multiple quantum wells

A detailed calculation of the index refraction of various GaAs-AlAs superlattices is presented for the first time. The calculation is performed by using a hybrid approach which combines the k-p method with the pseudopotential technique. Appropriate quantization conditions account for the influence of the superstructures on the electronic properties of the systems. The results of the model are in very good agreement with the experimental data. In comparison with the index of refraction of the corresponding AlGaAs alloy, characterized by the same average mole fraction of Al, the results indicate that the superlattice index of refraction values attain maxima at the various quantized transition energies. For certain structures the difference can be as large as 2 percent. These results suggest that the waveguiding and dispersion relation properties of optoelectronic devices can be tailored to design for specific optical application by an appropriate choice of the superlattice structure parameters.

Kahen, K. B.↗
NASA NTRS1986

Optical constants of GaAs-AlGaAs superlattices and multiple quantum wells

The optical properties of GaAs-Al sub x Ga sub 1-xAs superlattices are calculated as a function of the frequency and superlattice structure. The comutations are performed using a partition method which combines the vectors k.p method with the pseudopotential technique. The influence of the super-structure on the electronic properties of the systems is accounted for by appropriate quantization conditions. The anisotropy and structure dependence of the dielectric constant result mainly from the contribution of the gamma region while the contributions of the other regions of the Brillouin zone are rather insensitive to the superlattice structure. The superlattice index of refraction values are shown to attain maxima at the various quantized transition energies, where for certain structures, the difference between the refractive indices of the superlattices and its corresponding Al sub x Ga sub 1-xAs alloy can be as large as 2%. In general results are in good agreement with the experimental data.

Kahen, K. B.↗
NASA NTRS1987

Optical investigation of highly strained InGaAs-GaAs multiple quantum wells

Low-temperature optical transmission spectra of several In(x)Ga(1-x)/GaAs strained MQWs with x = 0.13-0.19 and well widths of 85-213 A have been measured. The excitonic transitions up to 3C-3H were observed along with steplike structures corresponding to band-to-band transitions, identified as 1C-1L transitions. By fitting experimental results to the calculations, it is concluded that the light holes are in the GaAs barrier region (type II MQW), and the valence-band offset is determined to be 0.30. Attention is given to a possible system in which the transition from type I to type II for light holes might be observed.

Ji, G.↗
NASA NTRS1987

Index of refraction of GaAs-Al(x)Ga(1-x)As superlattices and multiple quantum wells

A theoretical study of the index of refraction of superlattices and its variation as a function of frequency and the superlattice parameters, i.e., layer width and AlAs composition, is presented. Gamma-region exciton and valence-band mixing effects are included in the model. It is found that these two effects have an important influence on the value of the index of refraction and that superstructure effects rapidly decrease for energies greater than the superlattice potential barriers. Because of the quasi-two-dimensional character of the Gamma-region excitons, the results indicate that the superlattice index of refraction can vary by about two percent at the quantized, bound-exciton, transition energies. Overall, the theoretical results are in good agreement with the experimental data.

Kahen, K. B.↗
NASA NTRS1990

Tunable Quantum-Well Submillimeter-Wave Oscillators

Tunable submillimeter-wave generator is layered (AI/Ga)As device. Frequencies adjusted via applied voltages. New device concept offers potential to make relatively compact, efficient local oscillators for heterodyne mixers in submillimeter radar and imaging systems, nondestructive testing, diagnosis of plasmas, airborne spectroscopy of atmosphere, detection of weapons and other contraband, and communications.

Maserjian, Joseph↗