High quality InP quantum dots with diameters ranging from 25 to 45 Å, have been prepared; these quantum dots (QDs) show high quantum yields for band-edge photoluminescence (lowest energy HOMO-LUMO transition). The wavelength of the blue-shifted band-edge emission ranges from about 575 to 730 nm depending on QD size. The quantum yield for photoluminescence is 30% at 300 K and 60% at 10 K; the multiexponential decay of this emission exhibits lifetimes ranging from 5 to 50 ns. Deep red-shifted emission due to trapping of carriers in defect states on the QD surface which exhibits lifetimes above 500 ns, has been eliminated by treating the QDs with a dilute solution of HF or NH4F.

Articles you may be interested inCharacterization of heavily carbondoped GaAs grown by metalorganic chemical vapor deposition and metalorganic molecular beam epitaxy

The energy band gap narrowing effect in heavily C-doped GaAs was investigated using photoluminescence spectroscopy. The band gap was determined over the hole density range 1017–4×1020 cm−3 at 10 and 300 K. The band gap data at low temperatures confirm the available theoretical calculations up to 1020 cm−3. An unexpected temperature dependence of the observed band gap at high doping levels is discussed on the basis of carrier-phonon interactions. We present an analysis of the band gap narrowing effect that can be used for nondestructive measurement of hole densities in the range 1017–4×1020 cm−3.

A hole concentration greater than 1020 cm−3 in GaAs has been achieved using a liquid CCl4 source for carbon in a low-pressure organometallic vapor phase epitaxy system. The resistivity and hole mobility measured at 300 K for a heavily carbon-doped (1.2×1020 cm−3) Hall sample made from a thin (180 nm) epitaxial layer were 8.0×10−4 Ω cm and 65 cm2/V s, respectively. Carbon-doped samples with excellent surface morphology were achieved using a V/III ratio of 22, and growth pressure and temperature of 80 Torr and 600 °C, respectively. A novel photoluminescence technique, based on band-gap shrinkage of heavily doped p+-GaAs, has been shown to be useful for nondestructive measurement of the hole concentration in submicrometer layers.

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