Al 0.44 Ga 0.56 N spacer layer to prevent electron accumulation inside barriers in lattice-matched InAlN/AlGaN/AlN/GaN heterostructures

Abstract

The barrier structure in lattice-matched InAlN/GaN heterostructures with AlGaN-based spacer layers grown by metal organic vapor phase epitaxy was studied by the capacitance-voltage ͑C-V͒ method. To investigate the characteristics under positive bias, an Al 2 O 3 overlayer was added. The C-V characteristic of a sample with an Al 0.38 Ga 0.62 N ͑5 nm͒/AlN ͑0.75 nm͒ double spacer layer exhibited an anomalous saturation at a value far below the insulator capacitance under positive bias, which indicated electron accumulation at the InAlN/AlGaN interface. The C-V characteristic of an alternative sample with a single Al 0.44 Ga 0.56 N ͑1.5 nm͒ spacer layer did not exhibit the anomalous saturation. © 2011 American Institute of Physics. ͓doi:10.1063/1.3578449͔A lattice-matched InAlN/GaN heterostructure provides a high-density two-dimensional electron gas ͑2DEG͒ due to the difference in spontaneous polarization at the interface without any doping.1,2 To enhance electron mobility, an AlN ultrathin layer has been used as a conventional spacer layer.3,4 Several reports have been published on the application of the InAlN/AlN/GaN structure to field-effect transistors ͑FETs͒ ͑Refs. 3-5͒ including normally off type FETs.5 A recent study, however, reported that the insertion of an Al 0.38 Ga 0.62 N / AlN double spacer layer improved surface flatness and electron mobility compared with those for a single AlN spacer layer.6 Since the band gap of an Al 0.38 Ga 0.62 N layer is smaller than that of a lattice-matched InAlN layer, electron accumulation might occur at the InAlN/AlGaN interface under positive bias, resulting in a reduction in the effective barrier thickness. Schottky barrier diodes are not suitable for investigating electron accumulation in the barrier layer under positive bias. One of the methods of clarifying electron accumulation inside the barrier layer is to measure capacitance-voltage ͑C-V͒ characteristics using samples with an insulator overlayer on the heterostructure. In this letter, the Al 0.38 Ga 0.62 N / AlN double spacer layer is reappraised. A sample with an Al 0.44 Ga 0.56 N single spacer layer is also investigated as an alternative structure, for preventing electron accumulation inside the barrier layer. Figure 1 shows the structures of the test samples. An Al 2 O 3 ͑10 nm͒ / In 0.17 Al 0.83 N ͑10 nm͒ / Al 0.38 Ga 0.62 N ͑5 nm͒/ AlN ͑0.75 nm͒/GaN ͑2 m͒ structure and an Al 2 O 3 ͑13 nm͒ / In 0.18 Al 0.82 N ͑12 nm͒ / Al 0.44 Ga 0.56 N ͑1.5 nm͒/GaN ͑2 m͒ structure were fabricated and tested. The fabrication process of the test samples was as follows. Heterostructures were grown by metal organic vapor phase epitaxy. For the cap-annealing process to form an Ohmic contact, a 20 nm thick SiN x layer was deposited by electron-cyclotron resonance chemical vapor deposition using a SiH 4 / Ar and N 2 gas mixture at 260°C. After opening a ring-shaped window by lithography and wet etching using buffered hydrofluoric acid ͑BHF, HF: NH 4 F=1:5͒ solution, a ring-shaped Ti/Al/Ti/Au ͑30 nm/50 nm/20 nm/100 nm͒ Ohmic electrod...

Structural, electronic and elastic properties of wurtzite-structured TlxAl1−xN alloys from first principles

“…In recent years, Group IIIA nitrides (i.e., aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN)) and their ternary alloys such as gallium aluminum nitride (Ga x Al 1 À x N), indium aluminum nitride (In x Al 1 À x N) and indium gallium nitride (In x Ga 1 À x N) have gained wide recognition [1][2][3][4][5] as the most promising optoelectronic materials due to their outstanding optical properties and excellent mechanical properties. However, further progress in optoelectronics requires the continuous development of new materials.…”