InGaN/GaN quantum wells (QWs) were grown by molecular-beam epitaxy on c-plane sapphire substrates. The growth of InGaN is carried out at 550 °C with a large V/III ratio to counteract the low efficiency of NH3 at that temperature and to promote the two-dimensional mode of growth. An In composition of 16%±2% was determined by high-resolution x-ray diffraction experiments. Room-temperature photoluminescence of InGaN/GaN single QWs can be obtained over the whole visible spectrum (from 0.4 to 0.66 μm) by varying the well thickness from 1 to 5 nm. These heterostructures exhibit very large Stokes shifts between the emission and the absorption edge energies.
Spectroscopic ellipsometry (SE) carried out at 300 K together with reflectivity measurements
performed from 5 to 300 K are used to determine the temperature dependence of the refractive index
of hexagonal GaN films between 360 and 600 nm. The refractive index is well described with a Sellmeier
dispersion law and its variation with temperature is given. Below the band gap, the three excitonic
features (labelled A, B and C) appearing in the reflectivity spectra are analysed within a multi-polariton
model which includes the spatial dispersion. The transition energy, broadening parameter and oscillator
strength are derived. The temperature dependence of A and B broadening parameters is analysed.
GaInN and GaN were grown by molecular beam epitaxy on c-plane sapphire using NH3. 9 K photoluminescence performed on both GaInN thin layers and GaInN/GaN multiple-quantum wells (MQWs) exhibits narrow emission (∼50 meV linewidths). Transmission electron microscopy images show sharp GaInN/GaN interfaces and homogeneous GaInN layers. Strong indium surface segregation is also evidenced. Light-emitting diodes were fabricated from 5×GaInN (25 Å)/GaN (35 Å) MQW heterostructures. The 300 K electroluminescence yields blue light at 440 nm.
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