Characterizing epitaxial growth
Contacts:
Kresten Yvind, DTU Fotonik, Nanophotonic devices, 4525-6366 (kryv@fotonik.dtu.dk)
Epitaxy is the process of growing perfect single crystalline layers on top of an existing crystal. Epitaxy forms the basis of all the light-emitting semiconductor components like LEDs, lasers and other lightmanipulating devices. The semiconductor used is typically multiple (e.g. ~20) layers of In1-xGaxAsyP1-y where x and y denotes the solid stoichiometry i.e. the composition of the crystal. At DTU Fotonik operate a metal-organic vapour phase epitaxy (MOVPE) machine (see below), where we can accurately control a chemical reaction on a semiconductor wafer to make “whatever” composition we want (we call it atomic Lego for engineers). This process is very complicated on a microscopic scale and we generally use calibration runs to determine how the parameters we can control, e.g. pressure, temperature, and flows of the different “atoms” relate to the atomic compositions (alloys) in the crystals we get out of it.
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| Left: MOVPE system in DTU Danchip. Right: Bandgap and lattice constant for different compound semiconductors. |
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| Left: PL map of calibration wafer. Right: X-ray map and curve from the same wafer. |
The project:
The main part of the project will be theoretical analysing measurement data. First you will perform (follow staff member) x-ray and photoluminescence mapping of epitaxial calibration wafers from our MOVPE machine. This takes place on automated equipment in the cleanroom. From this you will get maps of lattice mismatch and bandgap of the semiconductor. Next you will read the theory to analyse this data and implement Matlab code to perform this analysis. Finally you will relate the measured results to the controlled parameters during the growth.
Learning objectives:
Calculate mismatch and bandgap of compound semiconductor as function of compositions (e.g. x,y in In1-xGaxAsyP1-y)
Implement matlab code to read mismatch maps and extract compositions across the wafer for AlxGa1-xAs
Implement matlab code to read both mismatch and PL maps and extract compositions across the wafers (make maps of x&y)
Analyze dependence of solid stoichiometry on the growth conditions (compare multiple growth with different flows of the atomic precursors)
Bonus objective: Calculate growth-rate variation from multiple quantum well structures (two growth calibration).