Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation

Lee, In Hwan; Choi, In–Hoon; Lee, C. R.; Noh, Sam Kyu

doi:10.1063/1.119893

Cited by 115 publications

(61 citation statements)

References 17 publications

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“…11,12 The origin of this band gap transition is still the subject of speculation. [13][14][15][16] It is most likely due to defects caused by the Si-dopant 16,17 or unintentional O. 16 In our samples the intensity of this line is strong.…”

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confidence: 92%

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Lagemaat

Vanmaekelbergh

Kelly

2004

Applied Physics Letters

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The electric-field dependence of the charge-carrier dynamics in GaN was studied by measuring excitation spectra of the sub-band-gap (yellow) luminescence as a function of bias using a Schottky junction formed at the interface between the semiconductor and an electrolyte solution. At large bias, the contribution of free electrons and holes to the photoluminescence is significantly reduced due to the dead-layer effect. As a result, striking features are revealed in the spectra close to the fundamental absorption. These features are attributed to exciton decay via yellow luminescence Electrons and holes, generated by light within the depletion layer of a Schottky diode, are effectively separated by the electric field and the minority carriers are collected at the interface. Minority carriers created within a diffusion length of the inner edge of the depletion layer can also reach the junction; 1 if they are transferred across the interface one observes photocurrent in the external circuit. Only those carriers created by light with a penetration depth ͑1/␣͒ which is larger than the sum of the minority carrier diffusion length L and the thickness of the space charge layer W will recombine, either nonradiatively or radiatively. The intensity of the emitted light I PL is given by:where 0 is the absorbed photon flux and is the ratio of the rate of radiative recombination to the total recombination rate. Many systems have been shown to conform to the "dead-layer model." 2-4Among the III-V semiconductors GaN is rather exceptional in that its exciton binding energy is large ͑ജ25 meV͒. [5][6][7][8] The formation of strongly bound electronhole pairs might be expected to influence the charge-carrier dynamics within the space-charge layer of an illuminated Schottky diode. In the present work we have used photoluminescence and photocurrent measurements on the Schottky junction formed at a semiconductor/solution interface to study excitonic effects in the field-dependent dynamics of carriers in n-type GaN epitaxial layers. We report an anomalous peak in the onset of the excitation spectrum of the subband-gap luminescence indicating enhanced emission at large band bending. We argue that this effect is due to a contribution from exciton absorption which is observed because of two reasons: the large binding energy of excitons and the suppression of emission from free carriers as a result of the dead-layer effect.The GaN epitaxial layers were grown by MOCVD on sapphire substrates using a 30 nm AlN buffer layer to reduce stress. 9 The layers were co-doped with Si. The density of uncompensated donors was 6 ϫ 10 17 cm −3 . Ohmic contacts were deposited by microwave sputtering of Ti/ Al/ Ni/ Au ͑15/ 300/ 40/ 200 nm͒. The ͑0001͒ Ga-terminated surface was exposed to solution.9 A standard three electrode cell was used for the electrochemical experiments. All potentials are reported with respect to the standard calomel electrode. Reproducible clean electrode surfaces were obtained by dipping in HCl before each experiment. The electrolyte fo...

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confidence: 92%

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Lagemaat

Vanmaekelbergh

Kelly

2004

Applied Physics Letters

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“…Among others, the stress relaxation in Si-doped GaN and undoped GaN films has been the focus of a number of recent studies. 4,[9][10][11] The effect of silicon doping on the mechanism of stress relaxation and defect formation in GaN is still under discussion. Ruvimov et al 4 suggest that the thermal stress is partly relaxed by migration of threading dislocations, leaving additional misfit dislocations in the basal plane.…”

Section: Introductionmentioning

confidence: 99%

Structural and optical properties of Si-doped GaN

et al. 2000

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Structural and optical properties of Si-doped GaN thin films grown by metal-organic chemical vapor deposition have been studied by means of high resolution x-ray diffraction ͑XRD͒, atomic force microscopy, photoluminescence, photothermal deflection spectroscopy, and optical transmission measurements. The incorporation of silicon in the GaN films leads to pronounced tensile stress. The energy position of the neutral donor bound excitonic emission correlates with the measured stress. The stress induced near band gap luminescence shift is estimated to 19Ϯ2 meV/GPa. An increasing concentration of dopant impurities in the films leads to asymmetries of the XRD and photoluminescence spectra, which are probably related to a stress induced inhomogeneous distribution of dopants. Atomic force microscopy observations of surface modulation with increasing silicon doping support this latter statement. Transmission and photothermal deflection spectroscopy measurements are used to determine the band gap energy and Urbach energy of highly doped samples.

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“…An additional complication arises for AlGaN grown on sapphire, the most common substrate of choice, as the sapphire (linear thermal expansion coefficient α ~ 7.6x10 -6 k -1 ) exerts a compressive strain to the AlGaN layers (α ~ 5.6x10 -6 k -1 ) during cool down which tends to mask the grown-in tensile strain due to lattice mismatch. Most of the post-growth ex-situ strain characterizations [8][9][10][11][12][13] would in this case measure a combination of a tensile stress due to lattice mismatch and a compressive component due to thermal expansion mismatch. In an attempt to isolate these two competing factors by directly probing the grown-in strain, we have employed an in-situ stress/strain monitor based on wafer-curvature measurement [14].…”

Section: Introductionmentioning

confidence: 99%

Monitoring and Controlling of Strain During MOCVD of AlGaN for UV Optoelectronics

Han

Crawford

Shul

et al. 1999

MRS Internet j. nitride semicond. res.

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The grown-in tensile strain, due to a lattice mismatch between AlGaN and GaN, is responsible for the observed cracking that seriously limits the feasibility of nitride-based ultraviolet (UV) emitters. We report in-situ monitoring of strain/stress during MOCVD of AlGaN based on a wafer-curvature measurement technique. The strain/stress measurement confirms the presence of tensile strain during growth of AlGaN pseudomorphically on a thick GaN layer. Further growth leads to the onset of stress relief through crack generation. We find that the growth of AlGaN directly on low-temperature (LT) GaN or AlN buffer layers results in a reduced and possibly controllable strain.

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Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation

Abstract: Stress and wafer bending of a -plane GaN layers on r -plane sapphire substrates

Cited by 115 publications

References 17 publications

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Structural and optical properties of Si-doped GaN

Monitoring and Controlling of Strain During MOCVD of AlGaN for UV Optoelectronics

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