Optical properties of Si-doped GaN

Schubert, E. Fred; Goepfert, I. D.; Grieshaber, W.; Redwing, Joan M.

doi:10.1063/1.119689

Cited by 214 publications

(141 citation statements)

References 16 publications

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“…Although the reason for this discrepancy is not clear, it is probably from the contribution of the phonon replicas superimposing on a zero-phonon luminescence band. In the case of n-GaN:Si, there were weak shoulders in the Stokes sides of the main luminescence peaks [11]. In ZnO:Ga, on the other hand, the intensity of a one-phonon replica could be comparable to that of a zero-phonon peak, which leads to larger FWHMs.…”

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confidence: 97%

“…In n-type semiconductors, the trap recombination rate is proportional to N T p, whereas the radiative recombination rate is proportional to np = N D p. The ratio of radiative to nonradiative recombination rates is N D /N T [11]. If N T is independent of the doping concentration, radiative transitions increase with increase in doping concentration.…”

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confidence: 99%

“…3(b) show the Stokes shift that is difference between the PL peak and the absorption threshold. Both the enhancement are explained in terms of potential fluctuations caused by the random distribution of doping impurities [11]. It is thought that the localization of photocreated carrier due to the fluctuation determines the Stokes shift.…”

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confidence: 99%

“…These microscopic concentration fluctuations result in potential fluctuations. By taking the standard deviation of the potential fluctuation, the broadening of the near-bandedge transition was calculated [11], the result of which is used in this work. The full width at half-maximum (FWHM) is then given by;…”

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confidence: 99%

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Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Makino

Segawa

Yoshida

et al. 2004

Applied Physics Letters

176

107

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We investigated the optical properties of epitaxial n-type ZnO films grown on lattice-matched ScAlMgO4 substrates. As the Ga doping concentration increased up to 6×10 20 cm −3 , the absorption edge showed a systematic blueshift, consistent with the Burstein-Moss effect. A bright near-bandedge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.PACS numbers: 78.55. Et, 81.15.Fg, 71.35.Cc, Optical properties of ZnO are currently subject of tremendous investigations, in response to the industrial demand for shortwavelength optoelectronics devices. Production of high-quality doped ZnO films is indispensable for the device application. Photoluminescence (PL) is a sensitive and non-destructive method, the results of which provide a good indicator of material quality. Impurity-doping, defect, and surface profile both have influence to its broadening, Stokes shift, and radiative efficiency. Room-temperature (RT) near-bandedge (NBE) luminescence has not been observed in donor-doped ZnO except for lightlydoped ones despite the long research history of this material as a transparent conductive window [1,2,3,4]. Indeed when ZnO:Al films were grown on lattice matched substrates, detectable NBE PL could be observed only at 5 K. As pointed out by Ko et al., oxidation of the Al during the growth owing to its high reactivity may be responsible for that. On the other hand, Ga is less reactive and more resistive to oxidation. The covalent bond lengths of Ga-O is slightly smaller than that of Zn-O, which will make the deformation of the ZnO lattice small even in the case of high Ga concentration [2]. In this publication, we report observation of the RT NBE luminescence from ZnO:Ga epitaxial layers. The radiative efficiency, threshold energy and the linewidth of the near-band-gap optical transition are investigated as a function of doping density of Ga.Ga-doped ZnO samples were grown by laser molecular-beam epitaxy on the (0001)-plane of a ScAlMgO 4 substrate. The samples were grown at temperatures of 650 to 680 • C. The Ga doping was varied to achieve doping densities in the range of 8 × 10 18 to 6 × 10 20 cm −3 [5]. We used Fig. 2 of Ref. 6 for the conversion from prescribed Ga concentration. The photoluminescence measurements were performed using an He-Cd laser, with emission at 325 nm. The luminescence from samples was dispersed in a 0.3 m spectrometer and detected by a charge-coupled device. Absorption was measured by using a UV/visible spectrometer (Shimadzu, UV2450) [4].Figure 1(a) shows room-temperature near-bandedge photoluminescence spectra (left-hand side) in n-type Ga-doped ZnO samples wit...

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confidence: 97%

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confidence: 99%

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confidence: 99%

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Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Makino

Segawa

Yoshida

et al. 2004

Applied Physics Letters

176

107

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“…A peak at 3.4 eV is due to recombination of (donor-bound) excitons 8,10 or a band-band transition 11 . A strong band, with a maximum at 2.2 eV is usually referred to as the "yellow luminescence."…”

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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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Material properties of GaN grown by MOCVD

Liu

Feng

et al. 1999

Surf. Interface Anal.

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n‐Type GaN thin films grown by metal‐organic chemical vapour deposition (MOCVD) were studied using photoluminescence (PL), photoreflectance (PR) and Raman scattering. In the PL spectra, the peak position of the band‐edge transition shifts to the red side monotonically with increasing doping concentrations. It may be explained theoretically in terms of many‐body effects, namely the renormalization of the bandgap. In the meantime, the line width of the PL peak is increased monotonically with the doping concentration. The luminescence line broadening can be modelled in terms of potential fluctuations caused by the random distribution of doping impurities. In the PR spectra the magnitude decreases monotonically with increasing doping concentration. This result can be explained by a simple model based on an assumption that low‐density surface states exist in the surface of GaN. In the Raman scattering spectra, both A1(LO) mode and E2 mode were observed in the back scattering configuration. The A1(LO) mode shifted towards the high‐frequency side and broadened with an increase in carrier concentration. This phenomenon can be interpreted by the LO phonon being coupled to the overdamped plasmon in GaN. Copyright © 1999 John Wiley & Sons, Ltd.

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Optical properties of Si-doped GaN

Cited by 214 publications

References 16 publications

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Material properties of GaN grown by MOCVD

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