MediumGaAs.cc

Go to the documentation of this file.

#include <iostream>
#include <fstream>
#include <sstream>
#include <cmath>
#include <algorithm>
 
#include "MediumGaAs.hh"
#include "Random.hh"
#include "GarfieldConstants.hh"
#include "FundamentalConstants.hh"
 
namespace Garfield {
 
MediumGaAs::MediumGaAs()
    : Medium(),
      // bandGap(1.42),
      eMobility(8.8e-6),
      hMobility(3.2e-6),
      eHallFactor(1.05),
      hHallFactor(1.25),
      eTrapCs(1.e-15),
      hTrapCs(1.e-15),
      eTrapDensity(1.e13),
      hTrapDensity(1.e13),
      eTrapTime(0.),
      hTrapTime(0.),
      trappingModel(0),
      m_hasUserMobility(false),
      m_hasOpticalData(false),
      opticalDataFile("OpticalData_GaAs.txt") {
 
  m_className = "MediumGaAs";
  m_name = "GaAs";
 
  SetTemperature(300.);
  SetDielectricConstant(12.9);
  SetAtomicNumber(32);
  SetAtomicWeight(72.32);
  SetMassDensity(5.317);
 
  EnableDrift();
  EnablePrimaryIonisation();
  m_microscopic = false;
 
  m_w = 4.35;
  m_fano = 0.1;
}
 
void MediumGaAs::GetComponent(const unsigned int& i, std::string& label, double& f) {
 
  if (i == 0) {
    label = "Ga";
    f = 0.5;
  } else if (i == 1) {
    label = "As";
    f = 0.5;
  }
}
 
void MediumGaAs::SetTrapCrossSection(const double ecs, const double hcs) {
 
  if (ecs < 0.) {
    std::cerr << m_className << "::SetTrapCrossSection:\n";
    std::cerr << "    Capture cross-section [cm2] must positive.\n";
  } else {
    eTrapCs = ecs;
  }
 
  if (hcs < 0.) {
    std::cerr << m_className << "::SetTrapCrossSection:\n";
    std::cerr << "    Capture cross-section [cm2] must be positive.n";
  } else {
    hTrapCs = hcs;
  }
 
  trappingModel = 0;
  m_isChanged = true;
}
 
void MediumGaAs::SetTrapDensity(const double n) {
 
  if (n < 0.) {
    std::cerr << m_className << "::SetTrapDensity:\n";
    std::cerr << "    Trap density [cm-3] must be greater than zero.\n";
  } else {
    eTrapDensity = n;
    hTrapDensity = n;
  }
 
  trappingModel = 0;
  m_isChanged = true;
}
 
void MediumGaAs::SetTrappingTime(const double etau, const double htau) {
 
  if (etau <= 0.) {
    std::cerr << m_className << "::SetTrappingTime:\n";
    std::cerr << "    Trapping time [ns-1] must be positive.\n";
  } else {
    eTrapTime = etau;
  }
 
  if (htau <= 0.) {
    std::cerr << m_className << "::SetTrappingTime:\n";
    std::cerr << "    Trapping time [ns-1] must be positive.\n";
  } else {
    hTrapTime = htau;
  }
 
  trappingModel = 1;
  m_isChanged = true;
}
 
bool MediumGaAs::ElectronVelocity(const double ex, const double ey,
                                  const double ez, const double bx,
                                  const double by, const double bz, double& vx,
                                  double& vy, double& vz) {
 
  vx = vy = vz = 0.;
  if (m_hasElectronVelocityE) {
    // Interpolation in user table.
    return Medium::ElectronVelocity(ex, ey, ez, bx, by, bz, vx, vy, vz);
  }
  // Calculate the mobility
  double mu = eMobility;
  mu = -mu;
  const double b = sqrt(bx * bx + by * by + bz * bz);
  if (b < Small) {
    vx = mu * ex;
    vy = mu * ey;
    vz = mu * ez;
  } else {
    // Hall mobility
    const double muH = eHallFactor * mu;
    const double eb = bx * ex + by * ey + bz * ez;
    const double nom = 1. + pow(muH * b, 2);
    // Compute the drift velocity using the Langevin equation.
    vx = mu * (ex + muH * (ey * bz - ez * by) + muH * muH * bx * eb) / nom;
    vy = mu * (ey + muH * (ez * bx - ex * bz) + muH * muH * by * eb) / nom;
    vz = mu * (ez + muH * (ex * by - ey * bx) + muH * muH * bz * eb) / nom;
  }
  return true;
}
 
bool MediumGaAs::ElectronTownsend(const double ex, const double ey,
                                  const double ez, const double bx,
                                  const double by, const double bz,
                                  double& alpha) {
 
  alpha = 0.;
  if (m_hasElectronTownsend) {
    // Interpolation in user table.
    return Medium::ElectronTownsend(ex, ey, ez, bx, by, bz, alpha);
  }
  return false;
}
 
bool MediumGaAs::ElectronAttachment(const double ex, const double ey,
                                    const double ez, const double bx,
                                    const double by, const double bz,
                                    double& eta) {
 
  eta = 0.;
  if (m_hasElectronAttachment) {
    // Interpolation in user table.
    return Medium::ElectronAttachment(ex, ey, ez, bx, by, bz, eta);
  }
 
  switch (trappingModel) {
    case 0:
      eta = eTrapCs * eTrapDensity;
      break;
    case 1:
      double vx, vy, vz;
      ElectronVelocity(ex, ey, ez, bx, by, bz, vx, vy, vz);
      eta = eTrapTime * sqrt(vx * vx + vy * vy + vz * vz);
      if (eta > 0.) eta = 1. / eta;
      break;
    default:
      std::cerr << m_className << "::ElectronAttachment:\n";
      std::cerr << "    Unknown model activated. Program bug!\n";
      return false;
      break;
  }
 
  return true;
}
 
bool MediumGaAs::HoleVelocity(const double ex, const double ey, const double ez,
                              const double bx, const double by, const double bz,
                              double& vx, double& vy, double& vz) {
 
  vx = vy = vz = 0.;
  if (m_hasHoleVelocityE) {
    // Interpolation in user table.
    return Medium::HoleVelocity(ex, ey, ez, bx, by, bz, vx, vy, vz);
  }
  // Calculate the mobility
  double mu = hMobility;
  const double b = sqrt(bx * bx + by * by + bz * bz);
  if (b < Small) {
    vx = mu * ex;
    vy = mu * ey;
    vz = mu * ez;
  } else {
    // Hall mobility
    const double muH = hHallFactor * mu;
    const double eb = bx * ex + by * ey + bz * ez;
    const double nom = 1. + pow(muH * b, 2);
    // Compute the drift velocity using the Langevin equation.
    vx = mu * (ex + muH * (ey * bz - ez * by) + muH * muH * bx * eb) / nom;
    vy = mu * (ey + muH * (ez * bx - ex * bz) + muH * muH * by * eb) / nom;
    vz = mu * (ez + muH * (ex * by - ey * bx) + muH * muH * bz * eb) / nom;
  }
  return true;
}
 
bool MediumGaAs::HoleTownsend(const double ex, const double ey, const double ez,
                              const double bx, const double by, const double bz,
                              double& alpha) {
 
  alpha = 0.;
  if (m_hasHoleTownsend) {
    // Interpolation in user table.
    return Medium::HoleTownsend(ex, ey, ez, bx, by, bz, alpha);
  }
  return false;
}
 
bool MediumGaAs::HoleAttachment(const double ex, const double ey,
                                const double ez, const double bx,
                                const double by, const double bz, double& eta) {
 
  eta = 0.;
  if (m_hasHoleAttachment) {
    // Interpolation in user table.
    return Medium::HoleAttachment(ex, ey, ez, bx, by, bz, eta);
  }
  switch (trappingModel) {
    case 0:
      eta = hTrapCs * hTrapDensity;
      break;
    case 1:
      double vx, vy, vz;
      HoleVelocity(ex, ey, ez, bx, by, bz, vx, vy, vz);
      eta = hTrapTime * sqrt(vx * vx + vy * vy + vz * vz);
      if (eta > 0.) eta = 1. / eta;
      break;
    default:
      std::cerr << m_className << "::HoleAttachment:\n";
      std::cerr << "    Unknown model activated. Program bug!\n";
      return false;
      break;
  }
  return true;
}
 
void MediumGaAs::SetLowFieldMobility(const double mue, const double muh) {
 
  if (mue <= 0. || muh <= 0.) {
    std::cerr << m_className << "::SetLowFieldMobility:\n";
    std::cerr << "    Mobility must be greater than zero.\n";
    return;
  }
 
  eMobility = mue;
  hMobility = muh;
  m_hasUserMobility = true;
  m_isChanged = true;
}
 
bool MediumGaAs::GetOpticalDataRange(double& emin, double& emax, 
                                     const unsigned int& i) {
 
  if (i != 0) {
    std::cerr << m_className << "::GetOpticalDataRange:\n";
    std::cerr << "    Medium has only one component.\n";
  }
 
  // Make sure the optical data table has been loaded.
  if (!m_hasOpticalData) {
    if (!LoadOpticalData(opticalDataFile)) {
      std::cerr << m_className << "::GetOpticalDataRange:\n";
      std::cerr << "    Optical data table could not be loaded.\n";
      return false;
    }
    m_hasOpticalData = true;
  }
 
  emin = opticalDataTable[0].energy;
  emax = opticalDataTable.back().energy;
  if (m_debug) {
    std::cout << m_className << "::GetOpticalDataRange:\n";
    std::cout << "    " << emin << " < E [eV] < " << emax << "\n";
  }
  return true;
}
 
bool MediumGaAs::GetDielectricFunction(const double& e, double& eps1,
                                       double& eps2, const unsigned int& i) {
 
  if (i != 0) {
    std::cerr << m_className << "::GetDielectricFunction:\n";
    std::cerr << "    Medium has only one component.\n";
    return false;
  }
 
  // Make sure the optical data table has been loaded.
  if (!m_hasOpticalData) {
    if (!LoadOpticalData(opticalDataFile)) {
      std::cerr << m_className << "::GetDielectricFunction:\n";
      std::cerr << "    Optical data table could not be loaded.\n";
      return false;
    }
    m_hasOpticalData = true;
  }
 
  // Make sure the requested energy is within the range of the table.
  const double emin = opticalDataTable[0].energy;
  const double emax = opticalDataTable.back().energy;
  if (e < emin || e > emax) {
    std::cerr << m_className << "::GetDielectricFunction:\n";
    std::cerr << "    Requested energy (" << e << " eV) "
              << " is outside the range of the optical data table.\n";
    std::cerr << "    " << emin << " < E [eV] < " << emax << "\n";
    eps1 = eps2 = 0.;
    return false;
  }
 
  // Locate the requested energy in the table.
  int iLow = 0;
  int iUp = opticalDataTable.size() - 1;
  int iM;
  while (iUp - iLow > 1) {
    iM = (iUp + iLow) >> 1;
    if (e >= opticalDataTable[iM].energy) {
      iLow = iM;
    } else {
      iUp = iM;
    }
  }
 
  // Interpolate the real part of dielectric function.
  // Use linear interpolation if one of the values is negative,
  // Otherwise use log-log interpolation.
  const double logX0 = log(opticalDataTable[iLow].energy);
  const double logX1 = log(opticalDataTable[iUp].energy);
  const double logX = log(e);
  if (opticalDataTable[iLow].eps1 <= 0. || opticalDataTable[iUp].eps1 <= 0.) {
    eps1 = opticalDataTable[iLow].eps1 +
           (e - opticalDataTable[iLow].energy) *
               (opticalDataTable[iUp].eps1 - opticalDataTable[iLow].eps1) /
               (opticalDataTable[iUp].energy - opticalDataTable[iLow].energy);
  } else {
    const double logY0 = log(opticalDataTable[iLow].eps1);
    const double logY1 = log(opticalDataTable[iUp].eps1);
    eps1 = logY0 + (logX - logX0) * (logY1 - logY0) / (logX1 - logX0);
    eps1 = exp(eps1);
  }
 
  // Interpolate the imaginary part of dielectric function,
  // using log-log interpolation.
  const double logY0 = log(opticalDataTable[iLow].eps2);
  const double logY1 = log(opticalDataTable[iUp].eps2);
  eps2 = logY0 + (log(e) - logX0) * (logY1 - logY0) / (logX1 - logX0);
  eps2 = exp(eps2);
  return true;
}
 
bool MediumGaAs::LoadOpticalData(const std::string filename) {
 
  // Get the path to the data directory.
  char* pPath = getenv("GARFIELD_HOME");
  if (pPath == 0) {
    std::cerr << m_className << "::LoadOpticalData:\n";
    std::cerr << "    Environment variable GARFIELD_HOME is not set.\n";
    return false;
  }
  std::string filepath = pPath;
  filepath = filepath + "/Data/" + filename;
 
  // Open the file.
  std::ifstream infile;
  infile.open(filepath.c_str(), std::ios::in);
  // Make sure the file could actually be opened.
  if (!infile) {
    std::cerr << m_className << "::LoadOpticalData:\n";
    std::cerr << "    Error opening file " << filename << ".\n";
    return false;
  }
 
  // Clear the optical data table.
  opticalDataTable.clear();
 
  double lastEnergy = -1.;
  double energy, eps1, eps2, loss;
  opticalData data;
  // Read the file line by line.
  std::string line;
  std::istringstream dataStream;
  int i = 0;
  while (!infile.eof()) {
    ++i;
    // Read the next line.
    std::getline(infile, line);
    // Strip white space from the beginning of the line.
    line.erase(line.begin(),
               std::find_if(line.begin(), line.end(),
                            not1(std::ptr_fun<int, int>(isspace))));
    // Skip comments.
    if (line[0] == '#' || line[0] == '*' || (line[0] == '/' && line[1] == '/'))
      continue;
    // Extract the values.
    dataStream.str(line);
    dataStream >> energy >> eps1 >> eps2 >> loss;
    if (dataStream.eof()) break;
    // Check if the data has been read correctly.
    if (infile.fail()) {
      std::cerr << m_className << "::LoadOpticalData:\n";
      std::cerr << "    Error reading file " << filename << " (line " << i
                << ").\n";
      return false;
    }
    // Reset the stringstream.
    dataStream.str("");
    dataStream.clear();
    // Make sure the values make sense.
    // The table has to be in ascending order
    //  with respect to the photon energy.
    if (energy <= lastEnergy) {
      std::cerr << m_className << "::LoadOpticalData:\n";
      std::cerr << "    Table is not in monotonically "
                << "increasing order (line " << i << ").\n";
      std::cerr << "    " << lastEnergy << "  " << energy << "  " << eps1
                << "  " << eps2 << "\n";
      return false;
    }
    // The imaginary part of the dielectric function has to be positive.
    if (eps2 < 0.) {
      std::cerr << m_className << "::LoadOpticalData:\n";
      std::cerr << "    Negative value of the loss function "
                << "(line " << i << ").\n";
      return false;
    }
    // Ignore negative photon energies.
    if (energy <= 0.) continue;
    // Add the values to the list.
    data.energy = energy;
    data.eps1 = eps1;
    data.eps2 = eps2;
    opticalDataTable.push_back(data);
    lastEnergy = energy;
  }
 
  const int nEntries = opticalDataTable.size();
  if (nEntries <= 0) {
    std::cerr << m_className << "::LoadOpticalData:\n";
    std::cerr << "    Import of data from file " << filepath << "failed.\n";
    std::cerr << "    No valid data found.\n";
    return false;
  }
 
  if (m_debug) {
    std::cout << m_className << "::LoadOpticalData:\n";
    std::cout << "    Read " << nEntries << " values from file " << filepath
              << "\n";
  }
  return true;
}
}