Transmission electron microscopy of AlGaAs/GaAs quantum cascade laser structures

Quantum cascade lasers can be efficient infrared radiation sources and consist of several hundreds of very thin layers arranged in stacks that are repeated periodically. Both the thicknesses of the individual layers as well as the period lengths need to be monitored to high precision. Different transmission electron microscopy methods have been combined to analyse AlGaAs/GaAs quantum cascade laser structures in cross-section. We found a small parabolic variation of the growth rate during deposition, affecting the stack periodicity and a reduced aluminium content of the AlGaAs barriers, whereas their widths as well as those of the GaAs quantum wells agreed with the nominal values within one atomic layer. Growth on an offcut substrate led to facets and steps at the interfaces

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

We demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. We present the design, fabrication, and characterization of two dimensional photonic crystal cavities in GaInP and measure quality factors in excess of 7500 at 680 nm. We demonstrate full control over the spontaneous emission rate of InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode we observe a Purcell enhancement of similar to 8. (C) 2010 American Institute of Physics. [doi:10.1063/1.3510469

Femtosecond Alexandrite Laser with InP/InGaP Quantum-Dot Saturable Absorber

A semiconductor saturable absorber mirror (SESAM) passively mode-locked Alexandrite laser was demonstrated. Using an InP/InGaP quantum-dot saturable absorber mirror, pulse duration of 380 fs at 775 nm was obtained. The laser was pumped at 532 nm and generated 295 mW of average output power in mode-locked regime with a pump power of 7.3 W. To the best of our knowledge, this is the first report of a passively mode-locked Alexandrite laser using SESAM in general and quantum-dot SESAM in particular

Absorption coefficients in AlGaInP lattice-matched to GaAs

The absorption coefficient of AlGaInP lattice-matched to GaAs, across the composition range from AlInP to GaInP has been obtained from photocurrent versus wavelength measurements on seven homo-junction AlGaInP PIN diode structures. Due to the sensitivity of the photocurrent measurement technique, values of absorption down to 100 cm−1 have been determined close to the band-gap. From these, the bandgaps in this material system were extracted across the composition range and these corroborate data in the literature that shows the band-gap becoming indirect when the aluminium content, x>0.48

Femtosecond Alexandrite Laser with InP/InGaP Quantum-Dot Saturable Absorber

A semiconductor saturable absorber mirror (SESAM) passively mode-locked Alexandrite laser was demonstrated. Using an InP/InGaP quantum-dot saturable absorber mirror, pulse duration of 380 fs at 775 nm was obtained. The laser was pumped at 532 nm and generated 295 mW of average output power in mode-locked regime with a pump power of 7.3 W. To the best of our knowledge, this is the first report of a passively mode-locked Alexandrite laser using SESAM in general and quantum-dot SESAM in particular

InAs Photodiodes for 3.43 mu(text)m Radiation Thermometry

We report an evaluation of an epitaxially grown uncooled InAs photodiode for the use in radiation thermometry. Radiation thermometry measurements was taken using the photodiode covered blackbody temperatures of 50 °C-300 °C. By determining the photocurrent and signal-to-noise ratio, the temperature error of the measurements was deduced. It was found that an uncooled InAs photodiode, with the peak and cutoff wavelengths of 3.35 and 3.55 μm, respectively, measured a temperature of 50 °C, with an error of 0.17 °C. Many plastics have C -H molecular bond absorptions at 3.43 μm and hence radiate thermally at this wavelength. Our results suggest that InAs photodiodes are well suited to measure the temperature of plastics above 50 °C. When tested with a narrow bandpass filter at 3.43 μm and blackbody temperatures from 50 °C-300 °C, the InAs photodiode was also found to produce a higher output photocurrent, compared with a commercial PbSe detectors

Avalanche Noise in Al0.52In0.48P Diodes

Multiplication and avalanche excess noise measurements have been undertaken on a series of AlInP homojunction p-i-n and n-i-p diodes with i region widths ranging from 0.04 to 0.89 μm, using 442 and 460 nm wavelength light. Low dark currents of 1000 kV/cm. For a given multiplication factor, the excess noise decreased as the avalanche width decreased due to the dead-space effect. Using 460 nm wavelength light, measurements showed that a separate absorption multiplication avalanche photodiode with a nominal multiplication region width of 0.2 μm had an effective k (hole to electron ionization coefficient ratio) of ~0.3

High-Gain InAs Planar Avalanche Photodiodes

We report the fabrication of InAs planar avalanche photodiodes (APDs) using Be ion implantation. The planar APDs have a low background doping of $2 times 10^{14} {rm cm}^{-3}$ and large depletion widths approaching 8 μm. The thick depletion width enabled a gain of 330 to be achieved at −26 V at 200 K without inducing a significant tunneling current. No edge breakdown was observed within the APDs. The surface leakage current was found to be low with a gain normalized dark current density of 400 μAcm−2 at −20 V at 200 K

Gigahertz-clocked teleportation of time-bin qubits with a quantum dot in the telecommunication C Band

Teleportation is a fundamental concept of quantum mechanics with an important application in extending the range of quantum communication channels via quantum relay nodes. To be compatible with real-world technology such as secure quantum key distribution over fiber networks, such a relay node should ideally operate at gigahertz clock rates and accept time-bin-encoded qubits in the low-loss telecom band around 1550 nm. Here, we show that In As-In P droplet-epitaxy quantum dots, with their sub-Poissonian emission near 1550 nm, are ideally suited for the realization of this technology. To create the necessary on-demand photon emission at gigahertz clock rates, we develop a flexible-pulsed optical-excitation scheme and demonstrate that the fast driving conditions are compatible with a low multiphoton emission rate. We show further that, even under these driving conditions, photon pairs obtained from the biexciton cascade show an entanglement fidelity close to 90%, comparable to the value obtained under continuous-wave excitation. Using asymmetric Mach-Zehnder interferometers and our photon source, we finally construct a time-bin qubit quantum relay able to receive and send time-bin-encoded photons and demonstrate mean teleportation fidelities of 0.82 ± 0.01, exceeding the classical limit by more than ten standard deviations

InGaP electron spectrometer for high temperature environments

In this work, a 200 μm diameter InGaP (GaInP) p+-i-n+ mesa photodiode was studied across the temperature range 100 °C to 20 °C for the development of a temperature-tolerant electron spectrometer. The depletion layer thickness of the InGaP device was 5 μm. The performance of the InGaP detector was analysed under dark conditions and then under the illumination of a 183 MBq 63Ni radioisotope beta particle source. The InGaP photodiode was connected to a custom-made low-noise charge-sensitive preamplifier to realise a particle counting electron spectrometer. Beta spectra were collected at temperatures up to 100 °C with the InGaP device reverse biased at 5 V. The spectrum accumulated at 20 °C was compared with the spectrum predicted using Monte Carlo simulations; good agreement was found between the predicted and experimental spectra. The work is of importance for the development of electron spectrometers that can be used for planetary and space science missions to environments of high temperature or extreme radiation (e.g. Mercury, Jupiter’s moon Europa, near-Sun comets), as well as terrestrial applications