Electron transport properties and weak localization of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures were experimentally investigated. Samples with the Al_0.35GaN_0.65/GaN heterojunction were grown by ammonia molecular-beam epitaxy (MBE) on sapphire substrates under nitrogen-rich conditions. Electron concentration and mobility in 2DEG under the temperature 4.2 К were n_s = 1.7x10¹³ cm^-2 and μ = 2 000 cm²/Vs, respectively.

At the temperature of 4.2 К the δσ(B) experimental dependence the δσ(B) is described quite well by the quantum correction to the 2D system conductivity in the approximation of the effective length of phase coherence l^*_φ: δσ(B)=(αe²/2π²ħ) [Ψ(1/2+ħ/2Be(l^*_φ)²)–Ψ(1/2+ħ/2Bel²–2ln(l^*_φ/l)], where l is the transport free path, α is the system geometry parameter, Ψ(x) is digamma function.

However, at the temperature of 1.8 К it is impossible to approximate the experimental dependence δσ(B) in the measured magnetic field range by the above dependence with only one adjustable parameter l^*_φ. In weak magnetic fields, when l_B=(h/2πeB)^1/4>>l_φ=(2Dτ_φ)^1/2, the conductivity correction is ~ l⁴_φ/l⁴_B. When l_B is about l_φ, this correction is ~ ln(l_φ/l_B). So for two conductivity subbands the effective length of phase coherence is l^*i_φ=((l^*_φ1)⁴+(l^*_φ2)⁴))^1/4 in weak magnetic fields and l^*ii_φ=(l^*_φ1 l^*_φ2)^1/2 in large magnetic fields.

The fact that δσ(B) is well described by only one effective length at the high temperature can be explained by the inter subband scattering which results in averaging of the effective lengths.

The work is supported by RFBR (grants nos. 05-02-17259a, 05-02-16901-а)

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