A study on strong memory effects for Mg doping in GaN metalorganic chemical vapor deposition

Ohba, Yasuo; Hatano, Ako

doi:10.1016/0022-0248(94)91053-7

Cited by 99 publications

(48 citation statements)

References 10 publications

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“…19,20 Since similar flow rates of TESn and TEOS lead to a comparable incorporation of Sn and Si in the layers (see Figure 5), we can assume that both precursors have a similar decomposition efficiency and that a comparable amount of free Sn and Si atoms are present in the reaction atmosphere. A large part of these is supposed to be incorporated in the layers, but unreacted Si and Sn atoms are pushed by the carrier gas to the exhaust system.…”

Section: Discussionmentioning

confidence: 97%

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

Baldini

Albrecht

Fiedler

et al. 2016

ECS J. Solid State Sci. Technol.

230

148

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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...

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Section: Discussionmentioning

confidence: 97%

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

Baldini

Albrecht

Fiedler

et al. 2016

ECS J. Solid State Sci. Technol.

230

148

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“…For the Mg (p-type) series, six UV QWs were grown below a single green QW and separated by GaN barriers. Due to the memory effect of the precursor Cp 2 Mg [22], only a 100 nm thick GaN cap on top of the layer stack is doped with a constant magnesium concentration (see Fig. 2(b)).…”

Section: Experimental Approachmentioning

confidence: 99%

Towards quantification of the crucial impact of auger recombination for the efficiency droop in (AlInGa)N quantum well structures

Nirschl¹,

Binder²,

Schmid³

et al. 2016

Opt. Express

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Recent experimental investigations on the reduction of internal quantum efficiency with increasing current density in (AlInGa)N quantum well structures show that Auger recombination is a significant contributor to the so-called "droop" phenomenon. Using photoluminescence (PL) test structures, we find Auger processes are responsible for at least 15 % of the measured efficiency droop. Furthermore, we confirm that electron-electronhole (nnp) is stronger than electron-hole-hole (npp) Auger recombination in standard LEDs. The ratio of respective Auger coefficients is determined to be in the range 1 < C nnp /C npp ≤ 12. This asymmetry is shown to limit the detection efficiency of Auger processes in our PL-based approach.

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“…Although Mg is the most successful p-type dopant for GaN, high hole concentrations have been limited by many complications, including a low solubility of Mg into GaN, 1 a tendency of Mg to accumulate and segregate at surfaces, 2 formation of pyramid-shaped defects, 3 a memory effect of Mg in a growth chamber, 4,5 a high vapor pressure of Mg at low temperatures, 6 a low sticking coefficient of Mg on GaN, a deep ionization energy of Mg acceptors in GaN, 7 unintentional hydrogen and oxygen doping, 8,9 a significant compensation of Mg acceptors at high dopant concentrations, 1 and a drastic dependence of incorporation upon the growth regime or III-V ratio. 10,11 As a consequence, there is a narrow window of growth conditions, which yield electrically active p-type GaN.…”

Section: Introductionmentioning

confidence: 99%

Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

Burnham¹,

Namkoong²,

Look³

et al. 2008

Journal of Applied Physics

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The metal modulated epitaxy ͑MME͒ growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7 ϫ 10 20 cm −3 , leading to a hole concentration as high as 4.5ϫ 10 18 cm −3 at room temperature, with a mobility of 1. GaN,7 unintentional hydrogen and oxygen doping, 8,9 a significant compensation of Mg acceptors at high dopant concentrations, 1 and a drastic dependence of incorporation upon the growth regime or III-V ratio.10,11 As a consequence, there is a narrow window of growth conditions, which yield electrically active p-type GaN. Furthermore, even low or moderate hole concentrations are often not consistently obtained and are difficult to reproduce due to the Mg incorporation sensitivity to growth conditions. These complications result in large and varied resistances and mobilities in GaN-based devices that rely on p-type layers. If hole carrier concentrations were to be increased, and p-type doping of GaN standardized, these devices could benefit from better performance and better reliability.Despite the complications associated with Mg-doped GaN, current state-of-the-art reports show promising results and give a reference for comparison. Mg incorporation as determined by secondary ion mass spectroscopy ͑SIMS͒ has been reported to be as high as 8 ϫ 10 20 cm −3 for metal organic chemical vapor deposition 12 and 3.5ϫ 10 20 cm −3 for molecular beam epitaxy ͑MBE͒.13 However, above approximately ͑2 -3.5͒ ϫ 10 20 cm −3 , the Mg incorporation begins to decrease with increased Mg flux 13 and inverts Ga-polar films to N-polar. 14 M-plane ͑1010͒ oriented substrates have been used to achieve a hole concentration as high as p = 7.2 ϫ 10 18 cm −3 .15 Electrical characterization for current stateof-the-art films grown on c-plane substrates is shown in Table I. [16][17][18] Reasonably high hole carrier concentrations are in the range of ͑1-3͒ ϫ 10 18 cm −3 . However, hole concentrations have been reported to be as high as 6 ϫ 10 18 cm −3 , 18 although the carrier concentration was metastable and significantly reduced upon heating during measurement. The metal modulated epitaxy ͑MME͒ growth technique was developed to specifically address reproducibility issues. [19][20][21][22] The MME growth technique is characterized by a group-III ͑metal͒ flux much higher than the group-V source, which would normally lead to droplets. However, the metal shutter is modulated to avoid droplet buildup and therefore build and deplete the metal bilayer on the growth surface, yielding smoother surfaces, larger grain sizes, and better repr...

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A study on strong memory effects for Mg doping in GaN metalorganic chemical vapor deposition

Cited by 99 publications

References 10 publications

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

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

Towards quantification of the crucial impact of auger recombination for the efficiency droop in (AlInGa)N quantum well structures

Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

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A study on strong memory effects for Mg doping in GaN metalorganic chemical vapor deposition

Cited by 99 publications

References 10 publications

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

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

Towards quantification of the crucial impact of auger recombination for the efficiency droop in (AlInGa)N quantum well structures

Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

Contact Info

Product

Resources

About

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

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