I had quite a lot of expectations for this summer and they were all met, thanks by the wonderful people who run UC LEADS. So let me tell you some of them.

One of the reasons why I chose to do semiconductor research was to get a bit more lab-technique experience. I believe that it may due to me being close to graduating soon, but that can vary by major. I learned how to use atomic force microscopy (AFM), Nomarski imaging microscopy, how to measure semiconductor properties, honed some of my soldering skills, and many other lab techniques. The other thing that was incredibly satisfying was the project results!

My project focused on growing indium arsenide (InAs) on a gallium arsenide (GaAs) substrate for use of devices such as hard drives. The issue of InAs on GaAs is that the surface of InAs is usually rough and that causes a drop in semiconductor performance. Roughness comes from dangling GaAs atoms (referred as dislocations) that remain unconnected to the InAs atoms due to straining that the InAs layer experiences. This is due to mismatch of the lattice constants of InAs and GaAs of 6.1 Å and 5.6 Å, respectively. A simple way to say it, the gallium and arsenide atoms have more compact spacing than the atoms in the indium arsenide layer. This mismatch forces the InAs to strain, which eventually leads to defects and roughness. Since this type of straining depends on thickness of the InAs layer, we grew InAs with different thicknesses (this was done on a 500 nm GaAs buffer plus substrate). After we grew these samples, I took them to take AFM images and to measure their transport properties.

From left to right, the growth thickness of indium arsenide: 50 nm, 100 nm, 250 nm, and 500 nm

Those holes you see are the dislocations, which decrease in number as thickness increases. This will mean that semiconductor performance (measured by the electron mobility, which tells you how fast the conducting electrons are moving through the semiconductor) will increase. The question is, though, is the relationship between growth thickness and electron mobility. Below was surprising (to me, at least!):

Indium arsenide on gallium arsenide performance as a function of indium arsenide thickness

I (again, only speaking for myself!) did not expect it to be non-linear. Basically – in this case – the electron mobility doesn’t get much higher as thickness increases. I find it fantastic to find results such as these, especially since it can be used by members in the lab. This result made it great summer experience.

One of excellent suggestions that my mentor (Borzoyeh Shojaei) one that I will also recommend. If this is your second (or third, or fourth, etc.) lab, speak to your previous professors. It shows them your new skills, exciting results, and it will show them how much you developed ever since. This will indeed make it easier for them to recommend for other positions in their labs, in other people’s labs, in work, and in graduate school. You’ll surprise yourself how much you’ve changed too!