The global objective of GERTUD is to significantly improve the performance of Si based resonant tunnelling (RT) diodes while keeping a full compatibility with CMOS process. The innovative part of the project is the fabrication and characterization of double barrier heterostructures by lateral epitaxy of Ge or SiGe wells between nanometer thick SiO2 or Si3N4 tunnelling barriers. In the one year assessment phase the goal is to demonstrate the feasibility of the proposed approach and to fabricate test components for evaluating the electronic properties of Ge/dielectric RTD.
The performance of resonant tunnelling diodes built on Si/Ge quantum heterostructures are presently limited by the low height of the tunnelling barrier. The objective of this project is to design new RT devices by replacing the SiGe barriers by nanometer thick SiO2 or Si3N4 layers and to grow by lateral epitaxy a single Ge well between the ultra thin dielectric barriers.
More specifically the two specific objectives are:
i) to determine the most relevant materials parameters for growing Ge/dielectric double barrier heterostructures;
ii) to demonstrate a resonant tunnelling effect on these RTD prototypes. The long term objective is to improve significantly the performance of SiGe based RTD while keeping full MOS compatibility.
DESCRIPTION OF WORK
In the one year assessment period, the work will be focused on:
Objective 1: controlling the growth parameters to obtain Ge wells with a low density of defects. Our previous work and those recently published by Japanese and German groups on Ge dots epitaxially grown through ultra thin insulators will serve as references to our project. The thermodynamic conditions for lateral epitaxy starting from Ge "nanoseeds" grown through the ultra thin insulators will be determined for optimising the structural and electronic quality of the materials. Advanced structural analysis will be used as feedback tools to the optimisation process. Chemical elements, which promote the wetting of the Ge layer over the insulator, will be used in order to favour the 2D lateral growth instead of the 3D development of the Ge dots. The double barrier hetero- structures will consist of a 3-5 nm thick Ge quantum well surrounded by 1 nanometer thick SiO2 or Si3N4 barriers grown in the MBE apparatus. This part of the work will be done at CEA-Grenoble;
Objective 2: processing and testing Ge/dielectric double heterostructures RTD. The experimental characterization of RTD prototypes will be done by monitoring the current-voltage curves at various temperatures. The processing and the testing of the RTD will be done at Gutenberg University. The first goal is to measure the effect of the thickness in homogeneities on the transparency of the tunnelling barriers. The second objective is to measure a negative differential resistance effect at low temperature and then at 300K. Modelling of the tunnelling transport of Ge/dielectric RTD will be also performed in order to optimise the design of the devices.
The achievement of the second objective is the ultimate criterion for the successful demonstration of the proposed innovative approach. An extension of the project with additional partners bringing in complementary material technology and industrial expertise will be requested upon complet ion of these objectives.
Funding SchemeACM - Preparatory, accompanying and support measures
405 30 Goeteborg