Editors' Choice—Si- and Sn-Doped Homoepitaxial β-Ga₂O₃Layers Grown by MOVPE on (010)-Oriented Substrates

Abstract

We studied the growth of Si-and Sn-doped homoepitaxial β-Ga 2 O 3 layers on (010)-oriented substrates by metal organic vapor phase epitaxy (MOVPE). At optimal growth conditions (850 • C, 5 mbar) the layers were smooth with RMS roughness values of ∼600 pm. A microstructural study by transmission electron microscopy (TEM) revealed a very high crystalline perfection of the layers. No dislocations or planar defects were observed within the field of view of TEM. Using Si as dopant, the free electron concentration could be varied in a range between 1 × 10 17 and 8 × 10 19 cm −3 , while with Sn the doping range was restricted to 4 × 10 17 −1 × 10 19 cm −3 . This was explained by a pronounced Sn memory effect in the MOVPE reactor that hampers achieving low carrier densities and by incorporation issues that limit the doping efficiency at high Sn doping levels. The electron mobility for a given doping density increased from ∼50 cm 2 /Vs for n = 8 × 10 19 cm −3 to ∼130 cm 2 /Vs for n = 1 × 10 17 cm −3 independently of the dopant. These values match the best literature data relative to β- Transparent Oxide Semiconductors (TSOs) are an emerging class of materials, which combine high electrical conductivity with transparency down to the deep UV region.1,2 Among TSOs, monoclinic β-Ga 2 O 3 is one of the most interesting compounds thanks to a wide bandgap (∼4.8 eV) that leads to a calculated electric breakdown field strength of 8 MV/cm. 3,4 The most promising application of β-Ga 2 O 3 is in the field of high power electronics, where it is predicted to outperform the leading technology based on SiC and GaN. A key advantage of β-Ga 2 O 3 is that native substrates can be fabricated from bulk single crystals grown from the melt by Floating Zone (FZ), 5 Edge-Defined Film Fed Growth (EFG) 6 and Czochralski (CZ) 7,8 methods. The growth of homoepitaxial β-Ga 2 O 3 has been mainly investigated by molecular beam epitaxy (MBE), 9-11 and only rarely by metal organic vapor phase epitaxy (MOVPE).12-14 For both epitaxial techniques Schottky diodes and field-effect transistors have been realized. 15,16 The structural quality of (100) β-Ga 2 O 3 layers grown by MOVPE has been relatively poor so far, with maximum electron mobilities of ∼40 cm 2 /Vs, 13 contrary to values achieved for layers grown by MBE on (010)-oriented substrates that are comparable to those of bulk material (>100 cm 2 /Vs). 10 A further improvement of the growth of β-Ga 2 O 3 by MOVPE is desirable, since MOVPE is more suitable for large-scale production.Here we report on the MOVPE-growth of Si-and Sn-doped epitaxial β-Ga 2 O 3 layers on (010) β-Ga 2 O 3 substrates. We selected this substrate orientation to investigate whether it promotes the growth of layers with higher crystalline perfection. Moreover, thermal conductivity in β-Ga 2 O 3 is anisotropic with the highest value along the [010] direction (27.0 W/mK at RT) and the lowest one along the [100] direction (10.9 W/mK at RT). 17 Heat dissipation in devices fabricated on (010)-oriented substrates is then predicted to be a...

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

“…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 .…”

Ga vacancies and electrical compensation in β-Ga2O3 thin films studied with positron annihilation spectroscopy

“…The homoepitaxial growth resulted in single crystalline material. 9,10,11 Basic sample information can be found in Table I. The dopant concentration was measured using secondary ion mass spectrometry employing Si and Sn implanted bulk β-Ga 2 O 3 standards.…”

Enhancement‐Mode β‐Ga2O3 Metal‐Oxide‐Semiconductor Field‐Effect Transistor with High Breakdown Voltage over 3000 V Realized by Oxygen Annealing

“…The experimental critical electric field up to 5.2 MV cm −1 has been reported, which has already exceeded the theoretical values of GaN and SiC . The electron mobility higher than 100 cm 2 V −1 s of n‐type Ga 2 O 3 epitaxial layers has also been reported …”

“…Gallium oxide (Ga 2 O 3 ), which emerged as a new semiconductor material, has been given great attention due to its promising applications in high‐power and low‐loss power devices. All applications benefit from its ultrawide bandgap (4.5–4.9 eV) and high critical electric breakdown field (8 MV cm −1 ) . The experimental critical electric field up to 5.2 MV cm −1 has been reported, which has already exceeded the theoretical values of GaN and SiC .…”