weinberg_1979
=============

Z\. A\. Weinberg, G\. W\. Rubloff and E\. Bassous, "Transmission, photoconductivity, and the experimental band gap of thermally grown SiO2 films", Phys\. Rev\. B 19, 3107 \(1979\)

`Source record <https://github.com/LupoLab/optmat/blob/main/src/optmat/data/sources/weinberg_1979.toml>`__ · :doc:`Catalogue </the-data/sources>` · :doc:`Review register </register>`

DOI: `10\.1103/physrevb\.19\.3107 <https://doi.org/10.1103/physrevb.19.3107>`__

**Source kind:** measurement

**Recorded technique:** Thermally grown amorphous SiO2 on \(100\) silicon \(dry O2 at 1000 degrees C, dry O2 with 4\.5 % HCl, or wet oxidation at 800 degrees C\)\. Transmission 7\-14 eV through free membranes \(436, 1100 and 5110 A; Si3N4\-protected anisotropic etching of the substrate; thickness \+\-1 % by ellipsometry\), McPherson 225 monochromator with an H2 lamp, 8 A resolution, sodium\-salicylate detector; the absorption coefficient from the exact thin\-film transmission formula \(Appendix\), iterated from Philipp's k with Philipp's n fixed\. Photoconductivity of Al\-SiO2\-Si capacitors \(575\-3500 A; Al 160 A thick, a masked and shielded contact\), its spectrum and its dependence on the field at fixed photon energy \(2\.6\-11\.1 eV\)\. Diodes under 450\-1350 A oxide for photoluminescence and excitons \(pp\. 3109\-3115\)\.

**Materials in structured entries:** SiO2, SiO2\_quartz

**Dataset quantities:** band\_gap

**Contents:** 4 datasets; 0 formulas.

Curation notes
--------------

Pages 3107\-3117 are pdf pages 1\-11\. Identity checked against the first page\.

BAND GAP \(the paper's result\)\. 'we associate the change in curvature seen in Fig\. 9 with the SiO2 band gap and deduce that E\_g ~ 9\.3 eV\. This association and the 9\.3\-eV value are, obviously, subject to a more detailed modeling of the problem' \(p\. 3114\)\: the transition energy in the field dependence of the photocurrent \(yield against field, curvature change as for internal photoemission over a barrier\), proposed as 'the most direct experimental estimate of the band gap' of thermally grown \(amorphous\) SiO2, direct or indirect not specified \(p\. 3115\)\. Band\-structure values the paper cites for alpha\-quartz\: indirect 9\.2 eV and lowest direct 9\.8 eV \(Chelikowsky and Schluter\); 9\.8 eV direct for idealised beta\-cristobalite \(Ciraci and Batra\) \(p\. 3107\)\: theory, notes only\.

ABSORPTION EDGE \(figures only; not digitised\)\. Fig\. 3 transmission of the three membranes; Fig\. 4 the absorption coefficient 7\-14 eV of the 436\-A film against Philipp's Kramers\-Kronig alpha \(shifted by \+0\.075 eV to align the first peak, at 10\.45 eV\) and Powell and Morad's 580\-A film; Fig\. 5 the tail with Appleton et al\.'s points\. 'The accuracy of alpha in our data is estimated to be better than \+\-2% for the region where T \< 0\.2, which applies from about 9\.2 eV for the 5110\-A film to about 11\.3 eV for the 436\-A film\. Above 11\.3 eV the scattered light correction becomes appreciable and the error could be as high as 10%\. The reproducibility of alpha among membranes \.\.\. has been within \+\-5%' \(p\. 3111\); reliable only above ~9\.2 eV \(p\. 3111\)\. The tail 'extends down to at least 8\.4 eV' and is 'approximately exponential \.\.\. in the range ~9\.2 eV \< h nu \< ~10\.2 eV, corresponding to about 2 decades in alpha' \(Urbach\-like; p\. 3115\)\. Philipp's Table X k at 0\.11\-0\.13 um is taken from this work \(philipp\_1985/weinberg\_k, the only tabulation\)\. Figs\. 6\-9\: photoconductivity spectra \(575, 1015, 2310 A; field 2e6 V/cm\) and the field dependence at 2\.6\-11\.1 eV\. Photoluminescence yield upper limit ~1e\-4 at 10\.2 eV \(p\. 3115\)\. Barriers\: Al Fermi level to SiO2 conduction band 3\.15 eV; Si to SiO2 conduction band 3\.1\-3\.2 eV \(pp\. 3107, 3114\)\.

REVIEW OF EARLIER VALUES \(pp\. 3107\-3108, 3115\), as the paper states them\. Those with a single value and a clear material and kind are the reproduced datasets below; the others are recorded here only\: \- Goodman\: hole photoemission from Si into thermal SiO2, 4\.9 eV to the SiO2 valence band, with the 3\.1\-3\.2 eV conduction\-band offset 'a band gap of 8\.0\-8\.1 eV' \(a range, and photoemission\: the vocabulary's band\-gap kinds have no photoemission\)\. \- DiStefano and Eastman\: besides the 9\.0 eV photoconductivity gap \(dataset\), '8\.9 \+\- 0\.2 eV from photoemission of electrons from SiO2 into vacuum' \(threshold 10\.2 eV\); 'revised upward to 9\.3 eV if one assumes that the valence\-band edge of SiO2 lies at 10\.6 eV below vacuum' \(Ibach and Rowe\)\. \- Williams\: 8 eV, estimated from an early absorption measurement 'in quartz' \(Ref\. 16\) to 8\.44 eV \(crystalline or fused not said\)\. \- Powell and Derbenwick\: besides the ~9 eV edge \(dataset\), 'a band gap of 8\.8 eV from their measurements of hole trapping in thermally grown SiO2 films illuminated by vuv photons' \(a charging threshold; no kind fits\)\. \- Stephenson and Binkowski \(XPS\)\: limits 5\.55\-7\.8 eV \(alpha\-quartz\), 5\.05\-7\.3 eV \(fused silica\), up to 8\.3 eV \(OH\-rich silica\); criticised \(defects from vacuum milling\)\. \- Zakis et al\.\: electron\-hole creation 'above 12 eV'\. \- Appleton et al\. \(alpha\-quartz and vitreous SiO2\), following Mott\: 'a direct band gap of 10\.6 eV with the possibility of a lower indirect band gap of about 9 eV' \(a suggestion\)\. \- Mott\: first 'about 10\.6 eV', later 'about 9 eV', indirect, with 10\.45 eV a direct\-gap exciton \(review\)\. \- Kaminow et al\.\: the absorption edge of their dry silica 0\.2 eV above that of wet silica\.

**Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.

Datasets
--------

weinberg\_1979/band\_gap
~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "band_gap",
     "material": "SiO2",
     "table": "text",
     "quantity": "band_gap",
     "unit": "eV",
     "abscissa": "none",
     "use": "primary",
     "parameters": {
       "kind": "photoconductivity",
       "form": "film",
       "technique": "field dependence of photoconductivity"
     }
   }

1 inline points in the source record.

E\_g ~ 9\.3 eV of thermally grown \(amorphous\) SiO2, from the field dependence of the photoconductivity of Al\-SiO2\-Si structures \(Fig\. 9; abstract p\. 3107, Sec\. II C p\. 3114, Sec\. III p\. 3115\)\. 'subject to a more detailed modeling'; no uncertainty stated\.

weinberg\_1979/literature\_photoconductivity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "literature_photoconductivity",
     "material": "SiO2",
     "table": "text",
     "quantity": "band_gap",
     "unit": "eV",
     "abscissa": "label",
     "use": "reproduced",
     "reproduced_from": [
       "T. H. DiStefano and D. E. Eastman, Solid State Commun. 9, 2259 (1971)",
       "A. N. Trukhin, Phys. Status Solidi B 86, 67 (1978)"
     ],
     "parameters": {
       "kind": "photoconductivity"
     }
   }

3 inline points in the source record.

Earlier photoconductivity gaps as the paper states them \(pp\. 3107\-3108\)\. DiStefano and Eastman\: 'an interband gap of 9\.0 eV by fitting their photoconductivity spectra \(performed on a 5000\-A thermally grown SiO2 film\) to a parabolic absorption\-edge characteristic of an indirect gap' \(the paper finds the fit unreliable because of interference, p\. 3112\)\. Trukhin\: photoconductivity of crystalline quartz, fused silica and thermally grown films, 'a direct band gap of 12 eV and a lowest band gap of 9\.5 eV'; the paper judges these spectra erroneous \(LiF\-covered samples, inadequate shielding, p\. 3113\)\.

weinberg\_1979/literature\_optical
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "literature_optical",
     "material": "SiO2",
     "table": "text",
     "quantity": "band_gap",
     "unit": "eV",
     "abscissa": "label",
     "use": "reproduced",
     "reproduced_from": [
       "R. J. Powell and M. Morad, J. Appl. Phys. 49, 2499 (1978)",
       "R. J. Powell and G. J. Derbenwick, IEEE Trans. Nucl. Sci. 18, 99 (1971)"
     ],
     "parameters": {
       "kind": "optical"
     },
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

2 inline points in the source record.

Earlier absorption\-edge gaps as the paper states them \(pp\. 3108, 3115\)\. Powell and Morad\: 'a value of 8\.0 \+\- 0\.2 eV, which is the same threshold they find in the absorption coefficient, photoconductivity spectra, and positive charging effects of thermally grown SiO2 films' \(a square\-root fit of the absorption tail; the paper calls it 'very doubtful', p\. 3112\)\. Powell and Derbenwick 'used Philipp's results to conclude that the fundamental absorption edge of SiO2 is at approximately 9 eV'\. The uncertainty level of \+\-0\.2 is not stated\.

weinberg\_1979/literature\_quartz
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "literature_quartz",
     "material": "SiO2_quartz",
     "table": "text",
     "quantity": "band_gap",
     "unit": "eV",
     "abscissa": "label",
     "use": "reproduced",
     "reproduced_from": [
       "E. Loh, Solid State Commun. 2, 269 (1964)"
     ],
     "parameters": {
       "kind": "optical"
     }
   }

1 inline points in the source record.

'The earliest reflectance spectrum of SiO2 \(in the form of natural brazilian quartz\) was reported by Loh; he identified the first spectral peak \(~10\.4 eV\) as excitonic and crudely estimated the band gap to be above it, at about 11 eV' \(pp\. 3107\-3108\)\. Axis not stated\.

Formulas
--------

No formulas are recorded.

Corrections
-----------

No dataset errata are recorded in this source record.

Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register </register>` for the checks and decisions.