Demonstration of β-(Al_xGa_1−x)₂O₃/β-Ga₂O₃modulation doped field-effect transistors with Ge as dopant grown via plasma-assisted molecular beam epitaxy

Abstract

β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures were grown via plasma-assisted molecular beam epitaxy. The β-(AlxGa1−x)2O3 barrier was partially doped by Ge to achieve a two-dimensional electron gas (2DEG) in Ga2O3. The formation of the 2DEG was confirmed by capacitance–voltage measurements. The impact of Ga-polishing on both the surface morphology and the reduction of the unintentionally incorporated Si at the growth interface was investigated using atomic force microscopy and secondary-ion mass spectrometry. Modulation doped field-effect transistors were fabricated. A maximum current density of 20 mA/mm with a pinch-off voltage of −6 V was achieved on a sample with a 2DEG sheet charge density of 1.2 × 1013 cm−2.

Defect Formation Energies of Interstitial C, Si, and Ge Impurities in β‐Ga2O3

“…With a band‐gap in the range from 4.5 to 4.9 eV, a high breakdown field, and a tunable carrier concentration, β ‐Ga 2 O 3 represents an excellent candidate for deep‐UV devices, metal–oxide–semiconductor field effect transistors, and Schottky diodes . Experimentally, n‐type doping of β ‐Ga 2 O 3 has been achieved by various techniques . At variance, p‐type β ‐Ga 2 O 3 appears to be more difficult to realize, in accordance with density functional theory (DFT) studies …”

“…Silicon and carbon impurities occur unintentionally in most β ‐Ga 2 O 3 samples at concentrations of cm −3 . When the samples are intentionally doped with Si, donor concentrations around cm −3 can be achieved . Germanium impurities at concentrations of 10 17 cm −3 can be introduced in β ‐Ga 2 O 3 through intentional doping by means of various molecular beam epitaxy techniques .…”

Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

“…In spite of the early stage of development, promising device demonstrations have already been reported, including metal-semiconductor field effect transistors (MESFETs), 1 metal-oxide field effect transistors (MOSFETs), [2][3][4][5] Schottky diodes, [6][7][8][9] FinFETs, 12 delta-doped FETs, 13 and (Al 1-x Ga x ) 2 O 3 /Ga 2 O 3 modulation-doped field effect transistors (MODFETs) grown by plasma-assisted molecular beam epitaxy (PAMBE). 14,15 For these devices to evolve as theoretically predicted, controlled doping during epitaxy is critical and doping studies in b-Ga 2 O 3 are at an early stage for molecular beam epitaxy (MBE) growth. Promising n-type dopants for b-Ga 2 O 3 are Si, Ge, and Sn, since each is predicted to substitute on Ga sites.…”

Band Gap and Band Offset of Ga2O3 and (AlxGa<

“…It is available as large single crystals [6] suitable for high-quality epitaxial thin-film growth by metalorganic chemical vapor deposition (MOCVD) [7,8] and molecular beam epitaxy (MBE) [5,9]; It displays high breakdown electric field [1], and the Baliga figure of merit exceeds that of SiC and GaN [3]; It can be easily doped n-type, and band gap engineering can be accomplished by incorporating In and Al, adding great flexibility to device design. Modulation doping of (Al x Ga 1−x ) 2 O 3 /Ga 2 O 3 heterostructures can be used to separate the ionized donors in the (Al x Ga 1−x ) 2 O 3 layer from the conduction electrons in the Ga 2 O 3 layer [10][11][12][13], providing a boost to the electron mobility to about 500 cm 2 V −1 s −1 [10,14,15] by suppressing scattering from the ionized impurities. Simulated band diagrams and two-dimension electron gas (2DEG) profile of MODFETs based on (Al x Ga 1−x ) 2 O 3 /Ga 2 O 3 assumed that the discontinuity in the band offset appears solely on the conduction band [10].…”