1. 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

2. “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

3. 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

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