טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentCalahorra Yonatan
SubjectIII-V Nanowires: Growth, Properties and Devices
DepartmentDepartment of Electrical Engineering
Supervisor Professor Dan Ritter
Full Thesis textFull thesis text - English Version


Abstract


Semiconducting nanowires (NWs) are at the focus of extensive multidisciplinary research, where all aspects of NWs, i.e. growth, structure, and chemical/ mechanical/electrical properties, must be thoroughly examined for future realization of applicable NW devices. III-V semiconductors are studied and used alongside silicon based technology due to their optical and electronic properties. The exciting possibility offered by NW technology is that NW growth is nearly-free of lattice match considerations. This opens up two possibilities: III-V NWs implementation on Silicon, advancing towards monolithic optical devices on silicon, and growth of III-V NW heterostructures and compositions, unavailable at planar technology.

First, a new InP NW growth regime has been demonstrated, utilizing the growth substrate’s native oxide as a selective area mask. In addition, it was found that the native oxide mask prevents splitting of thin catalysts, a phenomena demonstrated when the native oxide is removed. By implementing a different growth regime, where instead of a native oxide layer, a SiN
x layer is used, this effect has been utilized to grow NWs from catalyst whose initial diameter was in the range of tens to hundreds of nanometers, once again without catalyst splitting. These results show potential in growing sub-100 nanometer NWs, from photolithography based catalyst.


Another part of this research consists of the analysis of metal-wrapped NWs, focusing on the electrostatics of the problem, and extracting properties such as Schottky barrier height. This included the analysis of NWs having a non-uniform radial doping profile; the existence of such profiles in NWs has many experimental evidence, and it is arguably an inherent property of some of the common NW growth processes. Another aspect examined is the image force barrier lowering (Schottky effect) in NW systems; this problem introduces a fundamental issue regarding the reference energies in the systems. Subsequently, the effects of a non-ideal metal-semiconductor interface, as reflected by Bardeen’s model, on NW systems were examined; this was done by numerically solving Poisson’s equation in the NW, self-consistently with the constraints at the interface set by the non-ideal model.


Finally, in accordance with the original goals of this research, two-terminal vertical NW devices were realized; among the devices studied were InP NW ensemble based Schottky diodes, single InAs NW Schottky diodes, and a substrate-NW based light emitting diode. The process to realize the devices was developed during this research, and is a platform for future work in the group in these subjects.