Thickness & Composition Goal: In situ measurement and control of optical nanostructures (QW, MQW, DBR, SLS) Thickness & Composition AlGaN GaN InGaN GaN AlGaN Typical MOCVD deposition environment requires photon-base techniques Candidates: Ellipsometry Reflectometry (interferometry) Tradeoffs are between complexity and utility J.R. Creighton

“Practical” state-of-the-art for in situ measurements of compound semiconductor 2D structures (QW, DBR, SLS) grown by MOCVD Reflectometry is in becoming a widely used tool to measure thickness, or growth rate /2n Mostly used in a “pre-growth” calibration mode, almost never in a closed-loop control mode Arsenides, phosphides: precision < 1%, accuracy <2% Nitrides about 2X worse Because of uncertainties in optical constants, Absolute measurements are often calibrated against ex situ methods Composition is still mostly determined by ex situ methods (e.g. XRD) J.R. Creighton

405 nm reflectance shows promise for determining AlGaN composition in situ 15% Al0.15Ga0.85N n = 2.612 k = 0.060 11% Al0.11Ga0.89N n = 2.638 k = 0.084 22% Al0.22Ga0.78N n = 2.537 k = 0.029 end 071403vb 1033C GaN n = 2.637 k = 0.246 GaN n = 2.638 k = 0.241 J.R. Creighton

Quantum dot structures represent an extreme challenge for in situ measurements InAs/GaAs, AFM J.R. Creighton Courtesy of Jeff Cederberg, Sandia