Theory of doping and defects in III–V nitrides

The properties of a broad 2.86 eV photoluminescence band in carbon-doped GaN were studied as a function of C-doping level, temperature, and excitation density. The results are consistent with a C Ga -C N deep donor-deep acceptor recombination mechanism as proposed by Seager et al. For GaN:C grown by molecular-beam epitaxy (MBE) the 2.86 eV band is observed in Si co-doped layers exhibiting high n-type conductivity as well as in semi-insulating material. For low excitation density (4 W/cm 2 ) the 2.86 eV band intensity decreases as a function of cw-laser exposure time over a period of many minutes. The transient behavior is consistent with a model based on carrier diffusion and charge trapping-induced Coulomb barriers. The temperature dependence of the blue luminescence below 150 K was different for carbon-contaminated GaN grown by metalorganic vapor phase epitaxy (MOVPE) compared to C-doped MBE GaN.

Section: B Defect Model For the Carbon-related Blue Luminescencementioning

confidence: 99%

Analysis of the carbon-related “blue” luminescence in GaN

Armitage

Yang

Weber

2005

“…In fact, the ECR-N 2 plasma process also achieved low interface state densities in the SiN x /n-GaN system. 17,35 Theoretical calculation 36,37 predicted the lowest formation energy of N vacancies among native point defects in p-GaN. One of the possible reasons for achieving a nearly flat band condition on the p-GaN surface is that the present ECR-N 2 remote plasma treatment may partially recover or terminate N-vacancy related surface defects, and lead to a reduction of surface states.…”

Section: B Effects Of Ecr N 2 -Plasma Treatmentmentioning

confidence: 99%

Effects of Mg accumulation on chemical and electronic properties of Mg-doped p-type GaN surface

Hashizume

2003

Chemical and electronic properties of Mg-doped p-GaN surfaces were systematically investigated by x-ray photoelectron spectroscopy ͑XPS͒ and Auger electron spectroscopy ͑AES͒. The doping density of Mg ranged from 3ϫ10 19 to 9ϫ10 19 cm Ϫ3 . The XPS and AES analyses revealed the accumulation of Mg for all the air-exposed and chemically treated p-GaN surfaces. The apparent density of Mg calculated from the XPS integrated intensity and the AES intensity was more than one order higher than the value in bulk determined by secondary ion mass spectroscopy. Mg accumulation as well as large amounts of oxides made up the disordered region on the p-GaN:Mg surfaces. Large surface band bending of 1.2-1.6 eV was found at the p-GaN surfaces even after treatment in KOH and NH 4 OH solutions, due to the existence of high-density surface states. It was found that electron cyclotron resonance assisted N 2 -plasma treatment at 300°C for 1 min is very effective in removing such surface disordered regions and reducing surface band bending.

“…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

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...