Mueller Er

Power and spatial mode measurements of sideband generated, spatially filtered, submillimeter radiation

The first coherent measurement of submillimeter-wave sideband generator (SBG) output power is reported here. This SBG utilizes a submillimeter laser, microwave synthesizer, and high frequency Schottky diode to produce tunable radiation. Record efficiency and output power (10.5 /spl mu/W) at a drive frequency of 1.6 THz has been obtained, and SBG radiation was efficiently separated from the laser driver with Si etalons. The power measurements were made using a dual CO/sub 2/-submillimeter laser system and two Schottky diodes, one as the sideband generator and one as the receiver. The SBG efficiency of four different models of University of Virginia (UVa) diodes were studied and the first measurement of the output mode of the sideband (without the unshifted laser present) was also performed. Finally, confirmation of the optimal parameters for coupling a Gaussian beam into a corner-reflector mounted Schottky diode is presented. >

Quantum well GaAs/AlGaAs shallow-donor far-infrared photoconductors grown by molecular-beam epitaxy

Photoconductors utilizing planar‐doped silicon shallow donors in GaAs quantum wells formed with AlGaAs barriers have been fabricated and measured to have far‐infrared (FIR) resonant‐wavelength responsivities of ∼1 V W−1, with noise equivalent power values of ∼1×10−7 W Hz−1/2 at 4 K. The technology makes possible the use of FIR photoconductive magnetospectroscopy to measure the well position of sheet‐doped silicon ions when incorporated at doping levels below 1×1016 cm−3. A comparison of the measured position of the ions with the intended position reveals a discrepancy that can be linked to the growth parameters used to produce the structure.

Generation of high repetition rate far‐infrared laser pulses

We report the generation of pulsed optically pumped far‐infrared (FIR) radiation with a repetition rate of 200 kHz. These pulses were obtained in a straightforward method by pumping a FIR resonator with a high repetition rate, rf‐excited, waveguide CO2 laser. Pulses approximately 50 ns wide were generated both at 432.6 μm in HCOOH, and 117.7 μm in CH2F2. The pulse width of the FIR radiation was studied as a function of the CO2 pulse width, and the relative delay between the two was measured. Based on this data we conclude that the FIR radiation was gain switched and of a duration which was a function of either the gain bandwidth of the FIR transition, or more likely the FIR cavity parameters.

Multiquantum-well detection of nanosecond far-infrared superradiant pulses at temperatures above 77k

Abstract A lightly doped GaAs/(Ga, Al)As multiquantum-well sample is shown to be a fast detector of 2–5-ns wide far-infrared (FIR) pulses in the wavelength range from 100 to 500 μm. The conditions for optimum bias, sign of the photosignal, and non-linearity in the low-temperature current-voltage curve suggest that the detection mechanism is hot-electron photoconductivity. The responsivity is optimum near liquid-helium temperature where the detector response time is 2 ns. Furthermore, we observe for the first time in quantum wells, long-wavelength IR detection at temperatures above 77 K with a superradiant pulse-width-limited response time of

Far‐infrared photoconductive magnetospectroscopy as a tool for studying shallow donor concentration profiles in wide GaAs/AlGaAs quantum wells

The feasibility of using far‐infrared photoconductive magnetospectroscopy to accurately determine the positions of shallow donors in multiple quantum well samples grown by molecular‐beam epitaxy has been investigated and the technique successfully applied to silicon donors in quantum wells at doping levels below 2×1016 cm−3. Theoretical spectra calculated using a combined segregation and diffusion model for predicting donor position along with a theory of mapping donor 1s→2p+1 transition energies to magnetic fields are in good agreement with experimental spectra. A new value for the segregation decay rate, 3.1 nm/decade, is indicated for Si donors in wide GaAs/AlGaAs quantum wells grown at a substrate temperature of 680 °C. This new tool which is effective in the doping range of 1×1014 to 2×1016 cm−3 complements capacitance–voltage (C–V) techniques and secondary ion mass spectrometry. The technique is also applicable to a variety of heterostructures.