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 Incoming links: Fundamental energy gap of GaN from photoluminescence excitation spectra by Bo Monemar

Past exam of the chemistry A course of the University of Cambridge / 2025 / Paper 2 / A10 / d / i / Solution 2026-10-20

Using

E_{γ} = h c / λ

and an ideal band-edge photon energy equal to the quoted gap,

λ_{α} = \frac{1239.84 eV nm}{3.4 eV} = 364.66 nm .

(1)

At low temperature an electron and hole can form a bound exciton. Its recombination releases approximately

E_{g} - E_{B}

, so its wavelength is longer than

h c / E_{g}

evaluated using the gap at that same temperature. GaN excitation and emission measurements resolve such excitonic transitions below the fundamental gap.^[ref]

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