1. Electron mobility in very low density GaN/AlGaN/GaN heterostructures M. J. Manfra,a) K. W. Baldwin, and A. M. Sergent Bell Laboratories, Lucent Technologies, 700 Mountain Avenue, Murray Hill, New Jersey 07974 R. J. Molnar and J. Caissie Massachusetts Institute of Technology, Lincoln Laboratory, 244 Wood Street, Lexington, Massachusetts 02420-9108

2. Sample MBE-1.5μm GaN MBE-1.5μm GaN 16nm Al 0.06 Ga 0.94 N 16nm Al 0.06 Ga 0.94 N 3 nm GaN 3 nm GaN Mesa-100 nm Mesa-100 nm Ohmic contact -Ti/Al/Ni/Au Ohmic contact -Ti/Al/Ni/Au annealed at 800 。 C 30Sec annealed at 800 。 C 30Sec Hall bar:wide-100μm Hall bar:wide-100μm long-2 mm long-2 mm SiO 2 -100nm SiO 2 -100nm Gate-( Ni 10 nm/Au 100 nm ) Gate-( Ni 10 nm/Au 100 nm )

3. (a) Measured 2DEG density at T=0.3 K as a function of gate voltageV g between 1 and −4.25 V. In this regime, n s vs V g is linear and well approximated by n e =1.23x10 12 +2.42x10 11 cm −2 *V g. (b) 2DEG sheet resistance as a function of electron density at T=0.3 K.

4. (Color) Mobility at T=0.3 K solid black curve is the experimentally measured mobility as a function of 2DEG density from,2x10 11 to, 2x10 12 cm −2. For comparison, the red line displays the function μ 1 ~ne 1.0 at low density and the blue line represents μ 2 ~n e −1.5 in the high-density regime. The open black squares are calculated from μ T =1/(μ 1 −1 + μ 2 −1 ).

5. Integer quantum Hall states (R xx ~0) As the gate voltage is changed from −1 to −3 V the 2DEG density is reduced from 9.8x10 11 to 5x10 11 cm −2. the integer quantum Hall state near 10 T (R xx =0) can be progressively shifted from n=4, to n=3, and to n=2

6. Summary Grown high mobility and low density AlGaN/GaN hetero-structure Grown high mobility and low density AlGaN/GaN hetero-structure At low electron density the mobility obeys a power-law dependence ( μ~n e 1.0 ) At low electron density the mobility obeys a power-law dependence ( μ~n e 1.0 )