The implications of spontaneous polarization effects for carrier transport measurements in GaN

Harris, J. J.; Lee, K J; Webb, J. B.; Tang, H.; Harrison, I.; Flannery, L.B; Cheng, T.S.; Foxon, C.T.

doi:10.1088/0268-1242/15/4/319

Cited by 25 publications

(20 citation statements)

References 9 publications

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“…By using the thermal step method, we have found a polarization charge of (1-6) × 10 -6 C/cm 2 in these layers [23], which is in good agreement with those reported by Harris et al [24]. Hence, these results are an additional argument in favor of the implication of the polarization effects on the transport carrier properties in GaN [24].…”

Section: Resultssupporting

confidence: 91%

Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN

Matoussi¹,

Boufaden

Guermazi³

et al. 2003

Physica Status Solidi (b)

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In this paper we report electron beam induced current (EBIC) measurements on Schottky diodes on undoped GaN samples grown by the metal organic vapor phase epitaxy method on porous silicon substrates. A 2D simulation model was applied to perform the theoretical EBIC profiles and to compare with the experimental one. A minority carrier diffusion length (L) for holes of 0.72 µm was measured in the space charge region, indicating constant diffusivity of 6.48 cm 2 /s and a lifetime coefficient of 0.8 ns. An increase of L is observed as the probe source is moved from the Schottky junction to the bulk material. This increase was related to the polarization effects that are preponderant in group III-nitride devices. Far from the depletion layer (greater than 0.91 µm) the measured current is produced by the reabsorbed recombination radiation process. This corresponds to an optical self-absorption coefficient of a p = 0.112 µm . The results show that the transport parameters depend on the growth technology.

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Section: Resultssupporting

confidence: 91%

Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN

Matoussi¹,

Boufaden

Guermazi³

et al. 2003

Physica Status Solidi (b)

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“…Its piezoelectric properties are the reason for its use in surface acoustic wave (SAW) devices [56]. With this respect ZnO is similar to GaN [57]. This means intrinsic stress, due to lattice mismatch and/or to growth defects could induce charges at grain barriers or extended defects leading to additional scattering.…”

Section: Discussionmentioning

confidence: 99%

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Ellmer

Mientus²

2008

Thin Solid Films

335

191

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Highly-doped indium-tin oxide films exhibit resistivities ρ as low as 1. . Thus the grain barrier trap densities of ZnO and ITO are significantly different, which seems to be connected with the defect chemistry of the two oxides and especially with the piezoelectricity of zinc oxide.Keywords Transparent conductive oxides, carrier transport, degenerate semiconductors, grain barriers, electron mobility 2 Therefore, in the present study the carrier transport processes in ITO and ZnO are compared in order to get a deeper understanding of the differences between these TCO materials. For this purpose conductivity and Hall mobility measurements on ZnO:Al and ITO films were undertaken for films deposited on amorphous as well as single crystalline substrates (sapphire) in order to determine the dominant scattering processes (ionized impurities, grain barriers, crystallographic defects). Our own data are compared with literature data reported for ZnO and ITO to show the general trends. Theoretical and semiempirical models are used to fit the experimental data and to derive characteristic material parameters for these three oxides. Introduction Theoretical modelsThe theoretical models on ionized impurity scattering were already reviewed in 2001 by one of the authors when estimating the mobility limit of highly-doped zinc oxide [3]. In the following a short summary is given to lay the basis for the further discussion.Ionized impurity scattering. This scattering process is caused by ionized dopant atoms and dominates for carrier concentrations above about 10 19 cm -3. An analytical expression for the mobility µ ii of degenerately doped semiconductors, taking into account the non-parabolicity of the conduction band, was given by Zawadzki [7] and refined by Pisarkiewicz et al. [6]:where the screening functionwith the parameter ξ np =1-m 0 */m*, which describes the non-parabolicity of the conduction band (m*, m 0 * -effective masses in the conduction band and at the conduction band edge, 4 respectively). The prefactor in equ. (1) The fit parameters µ max , µ min and µ min -µ 1 describe the lattice mobility at low carrier concentrations, the mobility limited by ionized impurity scattering and the clustering mobility, discussed above (see Table 2). . The ZnO mobility values were fitted using the empirical formula (3) and the fit parameters are summarized in Table 2 together with the corresponding values for silicon. In the transition region from lattice to ionized scattering for 5 . 10 16 < N < 5 . 10 18 cm -3 a large scattering of the experimental ZnO data can be observed. Therefore, the data have been fitted in analogy to the silicon data, which exhibit a much higher accuracy [14].However, the exact transition does not influence the conclusions much since we are interested predominantly in ionized impurity scattering in the region N > 10 19 cm -3 .5 Neutral impurity scattering. Neutral shallow-impurity scattering is often discussed in papers about transport in TCO films at room temperature [17,18]. The mobility due to ...

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“…Another possibility is that damage was introduced on either surface during the reactive ion etching. Other possibilities include an accumulation layer caused by an N-face polarization charge 16 or edge conductionthe samples were sawn into squares with no attempt to remove the resulting damage on the edges. For the 245-µm-thick sample studied, the sawn edges represent approximately 5% of the sample's surface area.…”

Section: Multiple Carrier Analysis Of Variable Magnetic-fieldmentioning

confidence: 99%

Characterization of multiple carriers in GaN using variable magnetic-field hall measurements

Swartz

Tompkins

Myers

et al. 2004

Journal of Elec Materi

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Variable magnetic-field Hall-effect measurements were performed on two thick GaN samples grown by hydride vapor-phase epitaxy (HVPE), one freestanding and one attached to the sapphire substrate. Results are compared to those obtained using the more standard, single magnetic-field Hall measurements. In both samples, a second low-mobility electron was indicated that significantly influenced interpretation of single-field Hall measurements, particularly at low temperatures. Extraction of the bulk carrier using fits to the variable-field Hall data allowed a more accurate determination of the temperature dependence of the bulk electrical properties and, hence, basic physical parameters. In addition, the quantitative mobility-spectrum analysis (QMSA) technique, reported here for the first time on GaN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness. Thus, even the "improved" results, based on modeling the multiple-carrier fitting (MCF) analysis, obtained in this study should be viewed with some suspicion, as they clearly represent an average over an electrically inhomogeneous sample.

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The implications of spontaneous polarization effects for carrier transport measurements in GaN

Cited by 25 publications

References 9 publications

Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN

Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Characterization of multiple carriers in GaN using variable magnetic-field hall measurements

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