טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHarush Eli
SubjectPhotoelectrochemical Phenomena in Gallium Nitride
DepartmentDepartment of Chemical Engineering
Supervisors Professor Yaron Paz
Professor Emeritus Yosef Salzman


Abstract

The III-N semiconductors, thanks to their wide and direct band gap, are ideal candidates for Opto-Electronic applications. However, the nitrides extremely high etch resistance, dry and wet etch methods are ineffective due to their low etch rates and structural damages. The wet photoelectrochemical etch technique is investigated.

In the work presented here, n-type GaN wafers were grown (by MOCVD) and characterized by the concentration and mobility of the charge carriers through the Hall method. Later, a gold stripes mask was deposited. The GaN samples were placed in KOH solution and illuminated by a He-Cd laser. The etch depth measurements, SEM pictures and the etch profile served as the etch characteristics.

In the described above experiments, it was found that:

  1. The etch rate is dependent upon the electrolyte concentration at a power of 0.6±0.15. The experimental etch rate constant was 105 μm/s. The overall etch rate was dependent upon reaction kinetics and also mass transfer influence, even at the highest Reynolds values. 
  2. The etched surface profile at low electrolyte concentrations (<0.15M) is a function of the distance from the mask stripes and the orientation of the mask stripes relative to the fluid flow. These differences in the etch depth are due to mass transfer influence, matching a computerized model results.
  3. During the experiments, a unique 5 stages morphology was recognized. A skeleton structure, on which whiskers grew, was found to be directly related to TD (threading dislocations) below, who capture holes in a non-radiant recombination center.