Semiconductor Defects

This is an attempt at creating a collection of defect parameters of semiconductors in plain text. The idea is that such a plain text file should reduce allow for everyone to be able to access the information for now and into the future.

The information currently stored in the repository is currently limited to Shockley Read Hall parameterization, which allow calculation of how electron and holes electronically interact with the defect.

Shockley Read Hall parameterization

The Shockley Read Hall parameterisation assumes that there is a level within the forbidden region in a semiconductor’s through which electrons and holes can pass. A schematic of such a defect is shown in Figure 1.

The Shockley Read Hall parameterization of a defect has three values, all of which should be assumed to be temperature dependent:

• E_d: The energy level of the defect. We capture this value as reported in literature. This is usually reported as a distance to another energy level, i.e. E_c, E_v, or E_i.
• σ_e: The capture cross section for electrons
• σ_h: The capture cross section for holes

A 4th value that is recorded as a SRH parameter is k. k is σ_e/σ_h. This is recorded as lifetime spectroscopy usually provides a measure of k rather than absolute capture cross sections.

TODO: ‘k’ is obviously poor notation, but it is currently the standard notation. This should be improved both here and in literature.

How information is stored

The information is stored in both the file structure and the finial text files within the repository. The file structure of the repository is illustrated in Figure 2. The repository has two nested folders, with the text file in the finial folder.

The naming convention for the file are now detailed. The first element written corresponds to the folder that the file is in. Following this all the elements are written in alphabetical order.

The crystal site abbreviation currently used are:

• s: substitutional
• i: interstitial

The abbreviations for the defect charge state are:

• aa: double acceptor. The defect can change been a net change of -2 and -1.
• a: acceptor. The defect can change been a net charge of -1 and 0.
• d: donor. The defect can change been a net charge of 0 and 1.
• dd: double donor. The defect can change been a net charge of 1 and 2.

The “.srh” file is an ASCII file written in plain text. The structure of its contents is described in the following subsection.

“.srh” file continence

The contents of the finial file, and naming convention is now described. There are all optional inputs. To have an entry the minimum is the params section.

The text file is written with a yaml syntax. This makes it both easy for a human and computer to read! An example is found in W_s_s.srh:

Graff1995_1:
  title: Metal impurities in silicon-device fabrication
  DOI: 10.1007/978-3-642-97593-6
  measurement_technique: Review, DLTS
  comments: Taken from table 1 in the appendix. The table only provides
      the majority carrier capture cross section. The majority carrier has
      been estimated from the position of the defect level. e.g. if higher
      than the intrinsic level, it is assume the majority carrier was electrons.
  params:
    Ed: Ev+0.41

The initial value Graff1995_1, is the author year notation commonly used for publications. The _1 indicates that in the same publication two values were published for this impurity. If there author year notation is not unique the second name is appended with a letter rather than a number, e.g. Graff1995_a.

title

The title of the paper publication.

DOI

The Digital Object Identifier (DOI) for the file.

ISBN

The international standard book number.

sample

Sample provides a nested heading to provide sample details. This include the growth of the material, the dopant, and the resistivity (Ω.cm). An example is:

sample:
  growth: CZ
  dopant: boron
  resistivity: 1
  incorporation: ion implantation

TODO: The problem with this notation is when several samples are used. A better way is to recorded this information.

measurement_technique

There are a range of techniques that have been used to determine these defect properties. If several techniques are used, they are just comma separated. These are recorded in the repository using the following abbreviation:

2. DLTS: Deep level transient spectroscopy. There are many varients on DLTS, again these are separated by providing different suffixes, being:
   • O - optical DLTS.
   • L - Laplace DLTS
   • D - Double correlations DLTS
3. Hall: Temperature dependent ionized dopant concentration via the hall effect.
4. Photocurrent: Measurement of the current from a device. Suffixes include:
   • S - spectral
5. PC: Measurement of the photoconductivity from a device. Suffixes include:
   • S - spectral
   • T - measurement of trapping time constants
6. LS: Lifetime spectroscopy. This can be performed in different ways. These ways are depicted as suffixes, being:
   • D - doping dependent,
   • I - represents Injection dependent,
   • N - samplings with varying number of defects. Unlike other techniques the number of defects affects the measured value.
   • T - temperature dependent,

comments

Any comments about the file that maybe helpful.

params

This contains the published SRH parameterisation. As stated before the Shockley Read-Hall parameters captured are: “Ed” the energy level of the defect, “simga_e” the electron capture cross section, “sigma_h” the hole capture cross section, and “k” the ratio of the capture cross sections. k is captured as this is the value directly measured in lifetime spectroscopy, and thus allows easy entry into the database without the assumption of capture cross-sections from other publications. An example of an entry is:

params:
  Ed: Ev+0.3
  dEd: -0.1, 0.53
  sigma_h: "3.9e-16 * exp(-0.045/kT) "
  dsigma_h: 1e-13
  k: 10

The energy level of the defect is usually measured relative to the conduction band edge, or valence band edge. These values are recorded here in electron volts as “Ev+0.38”. The capture cross section are generally temperature dependent values, and reported in cm². The temperature dependence is using standard scientific notation, e.g. the temperature dependence of σ_h for interstitial iron acting as a donor is recorded under “sigma_h” as “3.9e-16 * exp(-0.045/kT)”. Published errors on these values are also able to be captured with the entry key being the parameter the the prefix “d”, e.g. the error in E_d is recorded under dE_d. Symmetric error values are recorded through listing a single number, while asymmetric errors are comma separated starting with the negativity error value. For example, to enter the error reports for Cobalt’s acceptor capture cross-sectional ratio (k) being -0.1 and +0.53, it is entered under the dk as “-0.1, 0.53”.