Germanium doping of self-assembled GaN nanowires grown by plasma-assisted molecular beam epitaxy

Abstract

Germanium doping of GaN nanowires grown by plasma-assisted molecular beam epitaxy on Si(111) substrates is studied. Time of flight secondary ion mass spectrometry measurements reveal a constant Ge-concentration along the growth axis. A linear relationship between the applied Ge-flux and the resulting ensemble Ge-concentration with a maximum content of 3.3×1020 cm−3 is extracted from energy dispersive X-ray spectroscopy measurements and confirmed by a systematic increase of the conductivity with Ge-concentration in single nanowire measurements. Photoluminescence analysis of nanowire ensembles and single nanowires reveals an exciton localization energy of 9.5 meV at the neutral Ge-donor. A Ge-related emission band at energies above 3.475 eV is found that is assigned to a Burstein-Moss shift of the excitonic emission.

Properties of GaN-based nanopillar-shaped crystals grown on a multicrystalline Si substrate

“…There have been some reports that the morphology variation is apparent due to high Ge density levels over 10 20 cm -3 . 23,25 The Ge density level of the sample grown with the Ge cell temperature of 1180 • C is estimated to be about 1×10 20 cm -3 , therefore; the morphology variation in this case is not unlikely. It has been also said that the variation originates in increases of lateral growth rates in heavily doped nanostructure crystals which are grown on single crystalline substrates.…”

“…Impurity doping is necessary to fabricate devices based on the nanopillar-shaped crystals. Therefore, Ge, which is widely used like Si as an n-type dopant in GaN, 23,24 was used to dope the nanopillar-shaped crystals during growth. The effects of this doping on the properties of the nanocrystals were investigated.…”

Long-lived excitons in GaN/AlN nanowire heterostructures

“…The GaN nanodisks were doped with Ge, using a beam equivalent pressure ranging from 0.5 − 1.5 × 10 −9 mbar. Ge was used as a dopant instead of Si as it introduces less strain in GaN being similar in size to Ga [35,36], and the change of the NW aspect ratio is negligible even for high Ge doping levels (3.3 × 10 20 cm [3]) [37]. The dopant concentrations of the samples under study, estimated from secondary ion mass spectroscopy measurements in reference samples [37], are summarized in Table I.…”

Photoelectrochemical reduction of carbon dioxide using Ge doped GaN nanowire photoanodes

“…13,36,37 The Ge effusion cell temperature was 1130 • C, which corresponds to Ge beam equivalent pressure (BEP) of ∼10 −11 Torr, which is similar the previous reports. 35,38 Due to the suitable atom size, Ge can be incorporated into GaN with less lattice distortion and can provide better nanowire morphology, compared to Si-doping. 38 In this study, both Ge-doped and nominally undoped GaN nanowires were studied.…”

“…35,38 Due to the suitable atom size, Ge can be incorporated into GaN with less lattice distortion and can provide better nanowire morphology, compared to Si-doping. 38 In this study, both Ge-doped and nominally undoped GaN nanowires were studied. samples, it is noted that there is no obvious difference of morphology induced by Ge doping.…”