Polarity of (00.1) GaN epilayers grown on a (00.1) sapphire

Seelmann‐Eggebert, M.; Weyher, J.L.; Obloh, H.; Zimmermann, H.; Rar, A.; Porowski, S.

doi:10.1063/1.120163

Cited by 190 publications

(116 citation statements)

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“…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.…”

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confidence: 99%

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: 99%

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Lagemaat

Vanmaekelbergh

Kelly

2004

Applied Physics Letters

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“…This first step is required because the c-plane {0001} is impervious to all chemical agents investigated, 12,13 except at defect sites where etch pits occur. 14,15 In the second step the semiconductor sample is immersed in a hot chemical etchant that is able to crystallographically etch GaN.…”

Section: Methodsmentioning

confidence: 99%

Fabrication of Smooth GaN-Based Laser Facets

Stocker

Schubert

Boutros³

et al. 1999

MRS Internet j. nitride semicond. res.

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A method is presented for fabricating fully wet-etched InGaN/GaN laser cavities using hotoenhanced electrochemical wet etching followed by crystallographic wet etching. Crystallographic wet chemical etching of n- and p-type GaN grown on c-plane sapphire is achieved using H3PO4 and various hydroxides, with etch rates as high as 3.2.μm/min. The crystallographic GaN etch planes are {0001}, {100}, {10}, {10}, and {103}. The vertical {100} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope (FESEM), indicating a surface roughness less than 5 nm, suitable for laser facets. The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction.

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“…A detailed study of the surface morphology of the GaN films with the different polarities [15] has revealed that the Ga-face (0001) surface is much smoother than the surface with N-polarity (000 1 ). Therefore, films with Ga-polarity are preferable for applications.…”

Section: Disscusionmentioning

confidence: 99%

CRYSTAL STRUCTURE AND DEFECTS IN NITROGEN-DEFICIENT GaN

Oktyabrsky¹,

Dovidenko²,

Sharma³

et al. 1999

MRS Internet j. nitride semicond. res.

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We have studied crystal structure and associated defects in GaN films grown on sapphire under nitrogen-deficient conditions by metalorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). The structural quality of the PLD films grown at 750 0 C was comparable with those grown by MOCVD at 1050 0 C having threading dislocations density of about 10 10 cm -2 at a film thickness 150-200 nm. Microstructure of the PLD films grown at temperatures above 780 0 C was found to be similar to that of nitrogen-deficient MOCVD films indicating the loss of nitrogen due to thermal decomposition of the nitride layers. Nitrogen-deficient MOCVD and PLD films exhibit polycrystalline structure with a mixture of cubic zinc-blende and wurtzite hexagonal GaN grains retaining tetragonal bonding across the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurtzite phase at different {111} planes of cubic GaN results in a rough and faceted surface of the film. Most of the stoichiometric films displayed (0001) Ga-face polarity, but the renucleated inclined wurtzite grains grew in the opposite N-face polarity. The major defects related to the cubic structural metastability are stacking faults and microtwins which being nuclei of the metastable cubic phase have an extremely low energy. We elucidate that the cubic phase is more stable under the nitrogen deficiency and, therefore, can exist without decomposition at higher nitrogen vacancy concentrations in the material.

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Polarity of (00.1) GaN epilayers grown on a (00.1) sapphire

Cited by 190 publications

References 10 publications

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Fabrication of Smooth GaN-Based Laser Facets

CRYSTAL STRUCTURE AND DEFECTS IN NITROGEN-DEFICIENT GaN

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