We present the growth, fabrication, and characterization of light-emitting diodes based on (Al,Ga)As quantum wells and dots embedded in a p-n GaP structure. Samples were grown on Sulphur-doped GaP (001) substrate using gas-source molecular beam epitaxy. The structures include either GaAs quantum structures with nominal coverage between 1.2 and 3.6 monolayers or Al0.3Ga0.7As quantum wells. For structures with GaAs layer thicker than 1.5 monolayers the 3.6% lattice mismatch in the materials system results in formation of quantum dots via Stranski-Krastanow growth mode with areal density of about 8×1010 cm-2. The atomic-force and transmission-electron microscopy show that with increasing coverage of GaAs from 1.8 to 3.6 monolayers the average lateral size and height of dots change in the range of 17-34 nm and 0.9–2 nm, respectively. The diode structures emit light from the red to the green spectral range up to room temperature. The GaAs/GaP QDs show electroluminescence between 1.8 eV and 2 eV, whereas the Al0.3Ga0.7As quantum wells emit light between 2 eV and 2.2 eV.
Optical nanocavities enable a strong interaction between single photons and single emitters. An appealing
application is the construction of a quantum interface for photonic and solid state qubits. Since the material of
the solid state qubit is often dierent from the nanocavity, there has been considerable interest in combining the
two in a hybrid architecture. We describe our recent development of such a hybrid interface based a Gallium
Phosphide photonic crystal nanocavity that is scanned and deterministically coupled to single emitters on a
surface. The technique is used to couple the cavity to the nitrogen vacancy center in diamond, an emitter system
with optically accessible electron spins and the ability to transfer electronic spin states to nuclear spins.
We investigated and demonstrated bio-medical imaging using a THz quantum cascade laser. With the THz quantum cascade laser (QCL) at 3.8 THz, we obtained large dynamic range and high spatial resolution in the transmission imaging technique. The various tissues images, such as lung, liver, and brain sections from the laboratory mouse were obtained and studied. The most important factor for this imaging scheme is to obtain high contrast with different absorption characteristics in tissues. We explored distinct images from the fat, muscles and tendon from the freshly cut tissues and investigated absorption coefficient and compared with FTIR measurement. We also demonstrated the image of distinct region of tumors progressed and normal tissues using this technique. The comparison of frequency dependent medical imaging with utilizing different wavelength of QCLs has been addressed.
We investigated and demonstrated bio-medical imaging using a THz quantum cascade laser. With the THz quantum cascade laser (QCL) at 3.8 THz, we obtained large dynamic range and high spatial resolution in the transmission imaging technique. The various tissues images, such as lung, liver, and brain sections from the laboratory mouse were obtained and studied. The most important factor for this imaging scheme is to obtain high contrast with different absorption characteristics in tissues. We explored distinct images from the fat, muscles and tendon from the freshly cut tissues and investigated absorption coefficient and compared with FTIR measurement. We also demonstrated the image of distinct region of tumors progressed and normal tissues using this technique. The comparison of frequency dependent medical imaging with utilizing different wavelength of QCLs has been addressed.
The growth, fabrication, and device characterization of the light-emitting diodes based on InP quantum-dot within a GaP matrix and on a GaP(100) substrate are described and discussed. The diode structures are grown using gas-source molecular beam epitaxy. Electroluminescence has been measured under a variety of bias conditions and temperatures. A green emission line at about 550 nm appears to result from carrier recombination in the strained InP wetting layer. Carrier recombination in the InP quantum dots results in red emission at about 720 nm.
The optical properties and associated carrier dynamics of self-organized InP quantum dots embedded in a GaP matrix are presented and discussed, together with their growth and structural properties. InP deposited on GaP (001) using gas-source molecular-beam epitaxy forms Stranski-Krastanow quantum dots for an InP coverage greater than 1.8 monolayers. The size of dots is dependent on the growth conditions; supercritical InP deposition under a sufficiently high phoshine flux results in relatively small (≈20 nm) and dense (≈ 5 × 109 dots/cm2) dots with intense optical emission. The photoluminescence from the quantum dots is observed up to room temperature at about 2 eV; photoluminescence from the strained two-dimensional InP wetting layer peaks at about 2.2 eV. Modeling based on the “model-solid theory” as well as time-resolved photoluminescence indicate that the band alignment for the InP wetting layer is indirect and probably type II; this emission results from spatially indirect recombination of electrons in the GaP X valley with holes in the InP and their phonon replicas. The band alignment of InP quantum dots, however, is type I. Whereas low-temperature time-resolved photoluminescence measurements indicate a rather long carrier lifetime of about 25 ns for the wetting layer, the carrier lifetime in the quantum dots is about 2 ns, typical for type-I quantum dots. Pressure-dependent photoluminescence measurements provide further evidence for a type-I band alignment for InP/GaP QDs at normal pressure, but indicate that they become type II under hydrostatic pressures of about 1.2 GPa and are consistent with an energy difference between the lowest InP and GaP states of about 31 meV. Exploiting the visible direct-bandgap transition in the GaP system could lead to an increased efficiency of light emission in GaP-based light emitters.
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