Electrical properties of β-Ga2O3 single crystals grown by the Czochralski method

Abstract

Electrical properties of nominally undoped β-Ga2O3 crystals grown by the Czochralski method from an iridium crucible under a carbon dioxide containing atmosphere were studied by temperature dependent conductivity and Hall effect measurements as well as deep level transient spectroscopy. All crystals were n-type with net donor concentrations between 6 × 1016 and 8 × 1017 cm−3. The Hall mobility of electrons was on average 130 cm2/Vs at room temperature and attained a maximum of 500 cm2/Vs at 100 K. The donor ionization energy was dependent on the donor concentration. Extrapolation of this dependence to zero concentration yielded a value of about 36 meV for isolated donors agreeing well with the ionization energy derived from effective-mass theory. Three deep electron traps were found at 0.55, 0.74, and 1.04 eV below the conduction bandedge. The trap at EC – 0.74 eV was detected in all samples with concentrations of 2 – 4 × 1016 cm−3. This concentration is comparable to that of compensating acceptors we have to take into account for an explanation of the temperature dependent electron density. Therefore, under the assumption that the electron trap at EC – 0.74 eV possesses acceptor character, this trap could be the dominating compensating acceptor in our crystals. Besides, a value of ΦB = (1.1 ± 0.1) V was determined for the Schottky barrier height of Ni on the (100) surface of n-type β-Ga2O3.

Electronic properties of the residual donor in unintentionally doped β-Ga2O3

“…Recent ab initio calculations 9 suggest that VO is a deep donor with the (2+|0) level located at The donor in UID β-Ga2O3 was previously suggested to be related to Si based on its presence in the source material with the concentration similar to the free carrier concentration determined from Hall-effect measurements 21 or from the Si-doping studies. 12,13 A recent study also shows that the free carriers activated by annealing in N2 gas are similar to the doped Si concentration.…”

“…19 Hall-effect measurements gave an estimated donor ionization energy in the range of 16-30 meV for conducting β-Ga2O3. 20,21 However, hybrid functional calculations suggested VO to be deep donors and, therefore, cannot be responsible for the n-type conductivity in UID materials. 9 Studies of UID β-Ga2O3 with the conductivity varying in a large range suggested that the Si impurity in the source material (β-Ga2O3 powder) can account for the observed conductivity.…”

“…9 Studies of UID β-Ga2O3 with the conductivity varying in a large range suggested that the Si impurity in the source material (β-Ga2O3 powder) can account for the observed conductivity. 21 The origin of the residual donor in UID material can have a strong impact on n-type doping of β-Ga2O3, since VO-related donors are expected to be less thermally stable than substitutional impurity donors and it can be more difficult to control the conductivity using an intrinsic donor. Understanding the electronic structure and clarifying the origin of the residual donor in UID β-Ga2O3 is of technological importance and also of interest from fundamental defect physics.…”

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

“…[1][2][3][4][5][6][7][8][9][10][11] Interest is also rising for possible applications as a deep ultraviolet solar blind detector due to its outstanding transparency out to $260 nm. 10,11 However, perhaps the primary driver for the interest is that b-Ga 2 O 3 , with its $4.5-4.9 eV bandgap, 2 is available as a bulk crystal, and therefore, native substrates are available for lattice-matched epitaxial growth of device structures, unlike contemporary wide and ultrawide bandgap semiconductors.…”

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…Measured electron mobilities are in the 100-200 cm 2 V −1 s −1 range at room temperature, up to about 500 cm 2 V −1 s −1 in the 100-200 K range for low-doped bulk material, [158,159] and up to even 5000 cm 2 V −1 s −1 at 80 K in high-quality HVPE-grown epitaxial layers. [160] As illustrated in Figure 8, mobility in Ga 2 O 3 appears to be limited by optical phonon scattering at high temperature and ionized impurity scattering at low temperature.…”