R. Germann

Energy dependence and depth distribution of dry etching‐induced damage in III/V semiconductor heterostructures

We have investigated the depth distribution, energy dependence, and the effect of the angle of incidence of ion beam etching (IBE) induced damage. Our technique is based on the partial etching of the upper GaAlAs barrier of a GaAs single quantum well (SQW) layer. The optical emission of the SQW at low temperatures is used as a local probe for the created damage. The dependence of the quantum efficiency on the etch depth can be described by a Gaussian depth distribution with a typical decay length of 5.6 nm and a non‐Gaussian long range tail. Our measurements show a strong dependence of the dry etch damage on the angle of incidence of the ion beam and on the sample orientation.

Nanometer lithography for III–V semiconductor wires using chloromethylated poly‐α‐methylstyrene resist

Chloromethylated poly‐α‐methylstyrene negative resist was investigated for its suitability in the fabrication of nanometer structures for optical studies. Investigating the photoluminescence efficiency of etched GaAs/AlGaAs wires we find a steep decrease with decreasing wire width, whereas for InGaAs/InP the decrease is much smaller. The difference in the behavior of the material systems can be explained by the effectiveness of surface recombination.

Transport and optical properties of semiconductor quantum wires

We have fabricated III–V semiconductor quantum wires which display a variety of novel transport and optical phenomena. For the definition of structures with widths down to 40 nm high resolution electron beam lithography and dry etching have been used. For the observation of dimensionality dependent effects in optical spectra buried quantum wires have been developed by overgrowth of dry etched structures and implantation induced intermixing. The physical properties of the nanometer structures have been analyzed by magnetotransport studies and emission spectroscopy.

Fabrication and optical characterization of quantum wires from semiconductor materials with varying In content

We have fabricated semiconductor wires from materials with varying In content and measured the quantum efficiency as a function of lateral wire width and temperature. The intensity decay observed for narrow wires can be explained by surface recombination at the wire sidewalls and the existence of an optically inactive layer. Sidewall recombination velocity as well as the width of the inactive layer are found to systematically depend on the In content.

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

In0.53Ga0.47As/InP quantum wires: Fabrication and magnetotransport studies

We have fabricated In0.53 Ga0.47 As/InP quantum wires with geometrical widths down to 80 nm by high resolution electron beam lithography and dry etching. The magnetotransport measurements display four distinct features: (1) The Shubnikov–de Haas oscillations show for narrow wires (<200 nm) a strong deviation from the 1/B periodicity. (2) Over the complete magnetic field range there are nonperiodic universal conductance fluctuations superimposed on the resistance curve. (3) At very low magnetic fields we observe a large negative magetoresistance, which decreases with increasing wire width. (4) In narrow wires we observe a distinct magnetoresistance peak at magnetic fields of about 1 T.

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.

Optical Emission from Quantum Wires

The physical properties of semiconductors with dimensions of the order of the de Broglie wavelength of electrons depend strongly on the device dimensions.1 In thin semiconductor heterostructures (quantum wells) the effective band gap is determined by the quantum well thickness in addition to the bulk properties of the quantum well material.2 This allows to increase the band gap in thin quantum wells by hundreds of meV if a suitable confinement material is employed. Furthermore the energy dependence of the density of states changes from a proportionality to E1/2 to a step function.

CW and time resolved luminescence study of dry etch damage in semiconductor wires

Abstract We have investigated the impact of dry etch sidewall damage on the optical properties of GaAs/AlGaAs quantum wires defined by high-resolution electron beam lithography. Spatially resolved cw and picosecond photoluminescence spectroscopy was used to characterize the dry etch damage at the wire sidewalls. Modeling the experimental results by solving the steady-state and time-dependent diffusion problems, we find that the sidewall effects can be described in terms of a sidewall recombination velocity and of an optically inactive, “dead” layer.

Magnetoresistance measurements in microstructured InGaAs/InP wires

Abstract Microstructured In .53 Ga .47 As wires with widths between 80nm and 50μm were fabricated from modulation doped heterostructures. All wires show a finite magnetoresistance down to 40mK. The resistivity (B = OT, T = 40mK) of the wires increases with decreasing wire width only about 4 times compared to the value at 50μm wire width, indicating only very small dry etch damage. The wires show a negative magnetoresistance for B⩽0.3T a distinct resistance maximum and reproducible resistance fluctuations (UCFs) at lower magnetic fields and Shubnikov-de-Haas oscillations at higher fields.