A. Forchel

The impact of p-doping on the static and dynamic properties of 1.5μm quantum dash lasers on InP

p-type modulation doping in the range of 0–100 acceptors per quantum dash (QDash) has been carried out to investigate the impact on QDash lasers on (100) InP. The differential gain was found to increase more than 50% for doping concentrations of 50 acceptors per QDash for constant cavity length lasers. However, this benefit is overcompensated by enhanced gain compression and enlarged thermal heating due to high internal losses in highly p-doped devices. The maximum modulation bandwidth of 8GHz in continuous wave operation at room temperature is, therefore, obtained for a moderate p-doping level of 10 holes per QDash.

Time resolved spectroscopy on etched GaAs/GaAlAs-quantum-microstructures

Abstract Using high resolution electron beam lithography and reactive ion etching, wires of GaAs/GaAlAs-quantum wells have been fabricated with widths between 5 μm and 0.5 μm. We have investigated the recombination luminescence of the charge carriers in time-resolved spectroscopy as a function of the wire width. We find a strong reduction of the recombination lifetime and a corresponding quenching of the luminescence intensity with decreasing wire width. This can be explained assuming nonradiative recombination via surface-levels as a very fast recombination mechanism. With a simple model we are able to describe the observed behaviour and obtain values for the surface-recombination velocity of about 3×105 cm/s

Metal wire definition by high resolution imprint and lift-off

Metal wires down to 25 nm width were fabricated using a simple imprint technology yet showing high resolution. The patterns were transfered with high geometric control from the silicon mold into a 100 nm thick PMMA layer by pressing the mold into the resist at a temperature of 140^oC for 20 min. Then the PMMA layer was thinned by Argon plasma etching and 10 nm thick Gold wires were defined by evaporation and lift-off. Similarly, by imprint in a three layer resist structure with an intermediate metal layer used as an etch stop 25 nm wide wires could be defined with larger process latitude.

Intermixed quantum wires with steep lateral confinement

Abstract We have developed quantum wires with width down to 40nm using high dose Ga - implantation (2×10 14 cm -2 ) in suitably masked GaAs/GaA1As quantum well substrates. Au masks with widths between 220nm and 40nm and a height of 40nm were defined by a two step lift-off process. The analysis of the luminescence spectra of the wires indicates a steep lateral potential which gives ririse to significant lateral quantization effects.

InxGa1-xAs/GaAs pseudomorphic quantum wells - growth and thermal stability

Abstract We have optimized the MBE growth conditions of InGaAs/GaAs pseudomorphic structures in order to obtain narrow emission linewidths and high quantum efficiencies. The thermal stability of the strained layers is studied using annealing at T ⩽930 °C. From the evaluation of the luminescence spectra after 30 min annealing we estimate an In/Ga interdiffusion length of about 2 nm at 900° C.

Well width dependence of the carrier life time in InGaAs/InP quantum wells

Abstract Investigations of the well width dependence of the radiative excitonic life time of InGaAs/InP quantum wells are reported, for well widths between 1 nm and 50 nm. The luminescence of the 1-1 transition of the quantum wells is detected via time resolved frequency up-conversion with the exciting Nd-YAG laser. In our experiments the time constants reveal an interesting phenomena with respect to the potential well thickness. For decreasing well widths we observe decreasing time constants of the excitonic recombination as has been observed for several other quantum well systems. But for well thicknesses below approximately 5 nm we find an increase of the life time with further decrease of the well widths. We explain the increase for small well widths by the reduced transition probability due to the delocalization of the envelope wavefunction of the electron in very small quantum wells.

High voltage electron beam lithography of the resolution limits of SAL 601 negative resist

Abstract We have investigated the suitability of SAL 601 for high voltage electron beam lithography. For exposure energies in excess of 100 keV resist lines with widths below 50 nm can be routinely defined. The resist masks have been used for the fabrication of quantum wires by wet etching.

Characterization of picosecond GaAs metal-semiconductor-metal photodetectors

Interdigitated GaAs metalsemiconductormetal Schottky photodiodes have been studied experimentally and theoretically. The time evolution of the response current has been measured by means of photoconductive and electrooptic sampling with a time resolution of 0. 8 and 0. 3 ps respectively. The response current to a 70 fs laser pulse reaches maximum within 25 p5 then shows a fast decay of about 10 ps followed by a slower one. Selfconsistent twodimensional Monte Carlo particle simulation predicts that the former is due to electrons the latter to holes. With a sufficiently strong electric field the two species of carriers get separated. With increased light intensity a screened plasma forms that vanishes only through recombination which takes of the order of nanoseconds.

Fabrication of nanometer width GaAs/AlGaAs/InP quantum wires

Abstract Starting from GaAs/AlGaAs and InGaAs/InP quantum well structures, we have produced quantum wires with lateral dimensions down to 30nm, using direct electron beam writing and several dry etching techniques. Investigating the photoluminescence efficiency of wire structures as a function of the linewidth we find a steep decrease with decreasing linewidth in the case of the GaAs/AlGaAs system, whereas for InGaAs/InP the decrease is much smaller. This luminescence decay can be interpreted as a result of the surface recombination at the sidewalls, which gains growing influence with decreasing linewidth.

Subthreshold swings below 60 mV/dec in three-terminal nanojunctions at room temperature

Subthreshold swings below the thermal limit of 60 mV/dec are demonstrated in a three-terminal nanojunction (TTJ) at room temperature. The T-shaped TTJ with a 50 nm wide center branch was based on a modulation-doped GaAs/AlGaAs heterostructure and was defined by electron-beam lithography and wet chemical etching. Operated as in-plane gated field-effect transistor, transistor characteristics were demonstrated. Efficient switching with subthreshold swings smaller than 40 mV/dec was observed. These findings are attributed to a dynamic gate capacitance which improves the switching properties of the device significantly.