Photoluminescence of bulk germanium

Abstract

We have performed photoluminescence (PL) measurements on intrinsic and doped bulk Ge substrates as a function of temperature and excitation power. A weak luminescence feature at 738 meV is observed at 7 K for Ge substrates with Al and Sb dopants, but not for intrinsic and Ga doped Ge. This feature can be explained by no-phonon (NP) assisted recombination of free excitons. Besides the NP feature, we observe intense luminescence peaks at 730 meV, 710 meV and 702 meV, which can be attributed to phonon assisted exciton recombination of transverse acoustic (TA), longitudinal acoustic (LA) and transverse optical (TO) phonons in the (111) direction, respectively. Besides these features, we observe luminescence at energy below 700 meV (1.77 μm). This luminescence shows much lower intensity (about 500 times) than the LA replica. The observed luminescence can be explained as a 2-phonon assisted recombination with the previously mentioned TA, LA and TO phonons with momentum in the (111) direction (at the L point) and a TO phonon at the Γ point. The power dependence of the integrated PL shows a log-log dependence with power factor of 2.02 at 9 K. This confirms that the PL originates from recombination of excitons, which are indirectly generated by creation of electrons and holes. The low energy PL edge follows the temperature dependence of the band gap as function of temperature, whereas the high energy PL edge shows an exponential broadening as function of temperature.

Direct and indirect band gaps in Ge under biaxial tensile strain investigated by photoluminescence and photoreflectance studies

“…The sample A peaks are centered at 0.725 eV (1710 nm) and 0.706 eV (1756 nm) at 80 K. k · p modeling of energy bands showed the the L valley to light holes (L-lh) transition with energy 0.746 eV. Measured peaks correspond to longitudinal acoustic (LA) and transverse optical (TO) phonon-assisted recombination, similar to that reported in [53]. At low temperature there are fewer free phonons in the crystal; phonon-assisted recombination from the L band generates a phonon.…”

Photoluminescence, recombination rate, and gain spectra in optically excited n-type and tensile strained germanium layers

“…However, most of the experimental work performed to study the spontaneous radiative recombination processes in Ge is carried out using photoluminescence (PL) techniques. [14][15][16] As a consequence, the excess carrier density and its spatial distribution inside the sample are not known a priori. Moreover, the experimentally observable external PL spectrum may substantially differ from the internal recombination rate spectrum due to selfabsorption processes, whose probability strongly depends on the emitted photon energy.…”

Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence

“…1(a) at 0.737 eV and 0.715 eV can thus be ascribed to recombination between holes at Γ and L-electrons mediated by transverse (TA) and longitudinal (LA) acoustic phonons, respectively. 36 By increasing the temperature these two PL bands redshift, leaking out [28]. (c) Temperature dependence of the total excess energy, ∆E, for carriers photoexcited in Ge by a laser energy at 1.165 eV (solid black line).…”