The influence of composition and unintentional doping on the two-dimensional electron gas density in AlGaN/GaN heterostructures

Abstract

We have studied the influence of Al content, AlGaN layer thickness, and unintentional background doping by oxygen on the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures. Hall measurements were made on samples grown with molecular beam epitaxy. The 2DEG densities in the range 2-3 ϫ 10 13 cm Ϫ2 were measured. A one-dimensional Schrödinger-Poisson model was used to describe the heterostructure. The calculations gave twodimensional electron densities in accordance with measured values. The electron density is very sensitive to the Al concentration in the AlGaN layer, whereas the sensitivity to layer thickness is small. Our simulations also showed that the two-dimensional concentration increased 50% when the free-carrier concentration changed from 10 15 cm Ϫ3 to 10 18 cm Ϫ3 . The relation between donor concentration and free-carrier concentration was found to agree when using oxygen ionization energy as a parameter.

Polarization Properties of Wurtzite III-Nitride Alloys Using the Hexagonal Reference Structure

“…The values from Susilo et al 53 and Smorchkova et al, 57 extracted from capacitance-voltage measurements, also show reasonable agreement with our simulation. Our predicted sheet charges seem to slightly underestimate (overestimate) the results of Davidsson et al 54 (Ng et al 56 ).…”

“…For (AlGa)N/GaN, Eq. 12 becomes: 53 Davidsson et al, 54 Arulkumaran et al, 55 Ng et al, 56 Smorchkova et al, 57 Jia et al, 58 Li et al, 59 Jho et al, 60 Lai et al 61 and Turchinovich et al 62 Some of these values are modified from field to charge for comparison. Data points in (c) are theoretical values obtained by Caro et al 17 and similarly for (InGa)N/GaN and (InAl)N/GaN.…”

“…Red dashed and blue dashed-dotted curves correspond to the simulation results of Dreyer et al 11 and Ambacher et al, 36 respectively. Data points in (a) and (b) are experimental values taken from: Susilo et al,53 Davidsson et al,54 Arulkumaran et al,55 Ng et al,56 Smorchkova et al,57 Jia et al,58 Li et al,59 Jho et al,60 Lai et al61 and Turchinovich et al62 Some of these values are modified from field to charge for comparison. Data points in (c) are theoretical values obtained by Caro et al17 See text for a thorough discussion.…”

Correct Implementation of Polarization Constants in Wurtzite Materials and Impact on III-Nitrides

“…2(b) may have several origins. There are experimental uncertainties that can influence fields, such as incomplete strain relaxation in buffer layers [42], and differences in background doping [43][44][45].…”