Quantentransport in III-V-Halbleiternanosäulen

The goal of this work has been to investigate und understand the electronic transport properties of vertical GaAs/AlAs nanocolumn resonant tunneling diodes (RTDs) and field effect transistors (RTTs) as well as of vertical InAs nanocolumn phase interference diodes. Using new top-down processing methods, these devices have been miniaturized to a scale not reached until now. The devices with the smallest lateral dimensions show new quantum transport phenomena which were not observed so far and can be used for developing of novel quantum device concepts. Besides the fabrication and electrical characterization of the devices, numerical calculations, simulations and quantum transport models represent the second important part of the work. GaAs/AlAs and InAs nanocolumns with lateral dimensions down to 30 nm have been processed by top-down approach. The nanocolumn definition is realized with the help of a high resolution electron beam resist Hydrogen-Silsesquioxan (HSQ). For the top metal semiconductor contact, a novel nonalloyed shallow ohmic contact based on low temperature grown (LTG) GaAs has been developed. HSQ is used also for sample planarization and physical isolation of the nanocolumns. In the preparation process of the RTTs, reproducible mask alignment accuracy of below 10 nm has been achieved and the vertical positioning of the all-around metal gate at the level of double barrier quantum well (DBQW) structure is realized with a precision of 10nm as well. Room temperature DC electrical measurements on the nano-RTDs show a distinct negative differential resistance in the I-V characteristics for devices down to 30 nm lateral dimension. Related to the lateral size of the nanocolumns, three different types of electronic transport can be distinguished, a classical one for column diameters >= 100 nm, a quantum-mechanical one for column diameter in the sub-100 nm range and space charge limited transport for the smallest processed nanocolumns. The miniaturization of the RTDs leads to the degradation of the transport properties, especially of the peak to valley current ratio (PVR), due to the increased surface scattering. However, the transport behavior changes for nanocolumns in the sub 100 nm diameter range. Apart from the main current peak, new substructures can be observed in the I-V characteristics. These are shoulder like features for columns with diameters between 80 nm and 100 nm but become clear peaks when the column diameters are in the 55-75 nm range. For sub-65 nm column lateral dimensions, a strong increase of the PVR and a sharp single peak is observed. A local maximum of the PVR of 3 is reached for columns with 50 nm diameter. The sub-40 nm devices show only space charge limited currents in the I-V characteristics. This behavior can be shifted to smaller or larger diameters by increasing or reduction of the channel doping. The multi-peak behavior as well as the improved PVR and sharper resonance can be attributed to a quantum collimation effect. For the smallest nanocolumns the lateral quantum confinement, caused by the low dimensionality of the system, leads to the formation of a 3D quantum-point-contact (QPC) in front of the DBQW structure. The quantization in this QPC depends on the column diameter and for a 50 nm column it exceeds the room temperature thermal broadening of the Fermi distribution function of about 25 meV. The new transport properties of these nanocolumns are explained further on with the help of single- and multi-mode quantum transport models. These are based on numerical calculations and simulations using a self-consistent semiclassical drift-diffusion solver. The comparison of the experimental results with those of the transport models shows a very high agreement. The measurements of the nano-RTTs indicate a good control of the device current by the gate voltage, without gate leakage. The peak current swing factor (the ratio between peak currents corresponding to the limits of a certain interval of the gate voltage) is about 3 for 150 nm diameter nano-RTTs but reach 6 for 60 nm diameter nano-RTTs (functionality based on the quantum collimation effect). Apart from GaAs/AlAs nanocolumns, InAs nanocolumns have been investigated as well. Nano-diodes were characterized by DC room temperature measurements and low temperature magneto-transport measurements. At room temperature, a linear behavior is observed in the I-V characteristics. Periodic oscillations of the resistance were measured by varying magnetic field at low temperatures. This behavior is related to interference effects, which result in the so-called Altshuler-Aronov-Spivak (AAS) resistance oscillations with magnetic field. Thus, for the first time AAS oscillations in semiconductor nanocolumns have been observed.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Wensorra, Jakob

Contributors dc:contributor

• Lüth, Hans

• info:eu-repo/classification/ddc/530
• Nanodraht
• Magnetowiderstand
• Galliumarsenid
• Galliumarsenid-Bauelement
• Nanotechnologie
• Quantenelektronik
• Nanoelektronik
• Quantenphysik
• Computersimulation
• Quantisierung <Physik>
• Molekularstrahlepitaxie
• Physik
• Quantentransport
• Nanofeldeffekttransistor
• Oberflächenzustände
• Nanosäulen-Resonanz-Tunneldioden
• RTD
• Nanosäulen-Feldeffekt-Resonanz-Tunneltransistoren
• RTT
• Nanosäulen-Phaseninterferenzdioden
• Silvaco
• Altshuler-Aronov-Spivak-Oszillationen
• nanowire
• surface states
• quantum transport
• nanotechnology
• quantum electronics
• whisker
• nanoelectronic
• quantum physics
• computer simulations
• e-beam lithographie

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113427%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51111