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Electrical and optical properties of heavily Ge-Doped AlGaN
摘要： We report the effect of germanium as n-type dopant on the electrical and optical properties of AlxGa1-xN layers grown by plasma-assisted molecular-beam epitaxy. The Al content has been varied from x = 0 to 0.66, confirmed by Rutherford backscattering spectrometry, and the Ge concentration was increased up to [Ge] = 1×1021 cm?3. Even at these high doping levels (> 1% atomic fraction) Ge does not induce any structural degradation in AlGaN layers with x < 0.15. However, for higher Al compositions, clustering of Ge forming crystallites were observed. Hall effect measurements show a gradual decrease of the carrier concentration when increasing the Al mole fraction, which is already noticeable in samples with x = 0.24. Samples with x = 0.64-0.66 remain conductive (σ = 0.8-0.3 Ω?1cm?1), but the donor activation rate drops to around 0.1% (carrier concentration around 1×1018 cm?3 for [Ge] ≈ 1×1021 cm?3). From the optical point of view, the low temperature photoluminescence is dominated by the band-to-band emission, which show only spectral shift and broadening associated to the Burstein-Moss effect. The evolution of the photoluminescence peak position with temperature shows that the free carriers due to Ge doping can efficiently screen the potential fluctuations induced by alloy disorder.
关键词： germanium doping,molecular-beam epitaxy,optical properties,AlGaN,electrical properties
更新于2025-09-19 17:15:36
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p-type doping of Ge by Al ion implantation and pulsed laser melting
摘要： Germanium recently attracted a renewed interest for its potential applications in several fields such as nanoelectronics, photonics, plasmonics, etc., but well-known issues about doping at high concentration and controlling impurity profiles prevent its integration in technology. To this purpose, p-type doping aluminum ion implantation followed by pulsed laser annealing in the melting regime has been investigated for the first time. In particular, two different regimes have been studied, in order to explore the limit of incorporation for such a method: 6.4 × 1014 Al/cm2 and 4.2 × 1015 Al/cm2, both at 25 keV, corresponding to concentrations below and above the solid solubility, respectively. We found that in the former case, oxygen contamination precludes full activation (< 60 %), as suggested by Raman characterizations. Besides, secondary ion mass spectrometry evidences pronounced out-diffusion and pile-up of the dopant near the surface. In the letter case, remarkable (～ 1 × 1020 Al/cm3), although partial (～ 30%), electrical activation is obtained, independently on O occurrence. Therefore, O-Al and Al-Al clustering are proposed as concurrent mechanisms, limiting full activation at high implanted dose. Nevertheless, the samples display good crystalline quality and, surprisingly, a significant thermal stability (up to 600° C).
关键词： Laser processing,Germanium,Doping,Ion Implantation,Aluminum
更新于2025-09-12 10:27:22
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High germanium doping of GaN films by ammonia molecular beam epitaxy
摘要： Doping Gallium nitride (GaN) with elemental Germanium (Ge) grown by ammonia molecular beam epitaxy is presented. Growth studies varying the GaN growth rate, substrate growth temperature and the elemental Ge flux reveal several incorporation dependencies. Ge incorporation increases with flux, as expected, and a doping range from ~1017 cm-3 to 1020 cm-3 was readily achieved. A strong substrate temperature dependence on the electrical properties of films grown is observed, with an optimal growth temperature of 740 °C, lower than standard GaN growth conditions for the ammonia molecular beam epitaxy. Compensation effects at higher growth temperatures are suspected, as observed with other techniques. Crystallographic defects are apparent at the highest doping concentrations from electrical and optical measurements, however thin layers of such highly doped films are of great interest for contact layers and tunnel junctions in devices.
关键词： Ammonia Molecular Beam Epitaxy,Molecular Beam Epitaxy,Tunnel Junctions,Germanium Doping,Gallium Nitride
更新于2025-09-04 15:30:14