AlGaN Nitride Epitaxial Growth & Bandgap Lab

Alloy Composition

Al fraction x in Al_xGa_1-xN 0.00

Growth Conditions

Substrate temperature 950 °C

V/III precursor ratio 2000

Live Readouts

Bandgap E_g

3.42 eV

Growth mode

step-flow

Growth rate

— nm/min

Film thickness

0 ML

Photon emission (e⁻–h⁺ recombination)
363 nm · near-UV

How it works

The scene grows a wurtzite Al_xGa_1-xN crystal one monolayer at a time on a hexagonal substrate mesh, mimicking MOCVD (metal-organic chemical vapor deposition) — the real process used to make GaN LEDs. Atoms are placed at lattice sites layer by layer with an ABAB wurtzite stacking sequence.

Vegard's law (with bowing):
Eg(x) = x·Eg(AlN) + (1−x)·Eg(GaN) − b·x·(1−x)
       = x·6.20 + (1−x)·3.42 − 1.00·x·(1−x)   [eV]

Emission wavelength:
λ = 1239.84 / Eg(x)   [nm]

Growth rate (precursor-limited, saturating in V/III):
R ∝ [V/III] / ([V/III] + K)      K ≈ 900

Surface diffusion length (Arrhenius):
L_D ∝ exp(−Ea / kT),  Ea ≈ 1.8 eV

Al fraction x — Vegard's law linearly interpolates the bandgap between GaN (3.42 eV, blue-violet) and AlN (6.20 eV, deep UV), with a bowing correction; atom color and the emission swatch update to the corresponding photon wavelength via E = hc/λ.
Substrate temperature — sets the adatom surface diffusion length. Below ≈900 °C diffusion is short, adatoms stick where they land and nucleate 3D islands ("island growth"); above it they diffuse far enough to fill each terrace before the next arrives, giving smooth atomic step-flow growth — visibly rougher vs. flatter crystal surfaces.
V/III ratio — the nitrogen-to-metal precursor supply ratio; growth rate rises with it but saturates once the metal (Ga/Al) precursor becomes the limiting reagent, exactly as in real MOCVD reactors.
Pause / Reset — freeze the deposition to inspect the lattice, or wipe the wafer and start a fresh growth run.

Real-world relevance: this Eg(x) tuning is exactly how blue (GaN), green, and deep-UV (AlGaN/AlN) LEDs and laser diodes are engineered — Shuji Nakamura, Isamu Akasaki and Hiroshi Amano won the 2014 Nobel Prize in Physics for cracking efficient blue GaN LEDs, which made white LED lighting possible.

Ga-rich atom Al-rich atom N atom

wurtzite Al_xGa_1-xN
MOCVD epitaxy

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