Ben Bowser

Erskine College
Advising Professor: Tim Sands
Project Title: Porous Anodic Alumina Ion Etch Masks

Introduction

Gallium Nitride is a material that shows much promise in the area of LEDs due to its high bandgap. Traditionally, GaN based LEDs are laced with Indium In order to change the bandgap and hence, the wavelength of light produced. It was hypothesized that an array of GaN crystal columns, which is ordered on a nano-scale will serve as an LED in which the wavelength of light produced is directly related to the diameter of the columns. In order to grow these columns an ordered fashion, a template of some sort must be used during the etching process. Porous Anodic Alumina is the ideal material for such an application, for during the anodization process, a nano-ordered array of pores is formed. When subjected to ion milling, the bases of these pore will be etched away, and then the ions will proceed to etch an ordered set of pits in the GaN. The Al will then be removed, and the pitted GaN sent to crystal growth in order to obtain the crystal columns desired.

Project Objectives

  • Produce a sample of Gallium Nitride which has an order set of pits etched into it

Experimental Approach

  • Anodization of aluminum films on a glass substrate in order to characterize the pore growth.
  • Deposition of Aluminum onto Gallium Nitride Substrate using an E-Beam Evaporator.
  • Anodization of these films.
  • Slightly etched films with NaOH in order to open the pores.
  • Pummeled the sample with Argon+ ions to etch through the aluminum into the Gallium Nitride.
  • Stripped remaining Aluminum away using HCl.

Research Findings

  • The anodization is very sensitive to the thickness of the aluminum film. The pores in very thin films (3-5 microns) do not end up near as ordered as those in thicker films typically do.
  • Characterized the pore formation from anodizing at different voltages, concentrations of Oxalic acid and
  • Helped to set equipment up and make procedure for anodization so results will be more reproducible.

Fig. 1. SEM picture of pores in anodized aluminum.
Fig. 2. AFM picture of pores as they begin to form.
Final Presentation