The “Quasidirect” Radiative Recombination of Free Holes at Neutral Shallow Donors in GaP

The luminescence band at 2.24 eV in n-type GaP is investigated in the temperature range of T = 27 to 120 K. It consists of a no-phonon line and several phonon replicas (TAX, LAX, TOX), which overlap with the donor–acceptor pair band. According to the analysis of the line shape and the energetic position of the intensity maximum in dependence of the temperature, the excitation intensity, and the time after excitation this band can be interpreted as being caused by free (hole)-to-bound (electron bound at the sulfur donor) transition. Taking into account the consequences of the GaP band structure on the symmetry properties of the bound electron states the free-to-bound transition is described as ‘quasidirect’. The calculated line shape is in good agreement with experiment using an indirect gap value which is 11 meV higher than accepted hitherto. The obtained indirect gap energy and free exciton binding energy are determined to Eg(T = 4.2 K) = (2.350 ± 0.002) eV and EFE = (22 ± 2) meV, respectively. In n-GaP wird die Lumineszenzbande bei 2, 24 eV im Temperaturbereich von T = 27, bis 120 K untersucht. Die Bande besteht aus einer Nullphononenlinie und ihren Phononensatelliten (TAX, LAX, TOX), die sich mit der Donator–Akzeptor-Paar-Bande uberlagern. Durch die Analyse der Linienform und der energetischen Lage des Intensitatsmaximums in Abhangigkeit von der Temperatur, der Anregungsintensitat und der Zeit nach der Anregung, kann diese Bande als ein free (Loch)-to-bound (Elektron am Donator Schwefel)-Ubergang interpretiert werden. Unter Berucksichtigung der Bandstrukturbesonderheiten von GaP und den daraus folgenden Konse-quenzen fur die Symmetrie des Elektronenzustandes am Donator, kann der free-to-bound-Uber-gang als ‚quasidirekt’ betrachtet werden. Unter Verwendung einer um 11 meV hoheren Energie-lucke als bisher angenommen wurde, ist die errechnete Linienform in guter Ubereinstimmung mit dem Experiment. Die indirekte Gapenergie und die Bindungsenergie des freien Exzitons ergeben sich zu Eg(T = 4,2 K) = (2,350 ± 0,002) eV bzw. EFE = (22 ± 2) meV.

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