code: def plot_zt_dop(self, temps='all', output='average', relaxation_time=1e-14):
          
          import matplotlib.pyplot as plt
          if output == 'average':
              zt = self._bz.get_zt(relaxation_time=relaxation_time,
                                   output='average')
          elif output == 'eigs':
              zt = self._bz.get_zt(relaxation_time=relaxation_time, output='eigs')
  
          tlist = sorted(zt['n'].keys()) if temps == 'all' else temps
          plt.figure(figsize=(22, 14))
          for i, dt in enumerate(['n', 'p']):
              plt.subplot(121 + i)
              for temp in tlist:
                  if output == 'eigs':
                      for xyz in range(3):
                          plt.semilogx(self._bz.doping[dt],
                                       zip(*zt[dt][temp])[xyz],
                                       marker='s',
                                       label=str(xyz) + ' ' + str(temp) + ' K')
                  elif output == 'average':
                      plt.semilogx(self._bz.doping[dt], zt[dt][temp],
                                   marker='s', label=str(temp) + ' K')
              plt.title(dt + '-type', fontsize=20)
              if i == 0:
                  plt.ylabel("zT", fontsize=30.0)
              plt.xlabel('Doping concentration ($cm^{-3}$)', fontsize=30.0)
  
              p = 'lower right' if i == 0 else ''
              plt.legend(loc=p, fontsize=15)
              plt.grid()
              plt.xticks(fontsize=25)
              plt.yticks(fontsize=25)
  
          plt.tight_layout()
  
          return plt
docs: Plot the figure of merit zT in function of doping levels for different
          temperatures.
  
          Args:
              temps: the default 'all' plots all the temperatures in the analyzer.
                     Specify a list of temperatures if you want to plot only some.
              output: with 'average' you get an average of the three directions
                      with 'eigs' you get all the three directions.
              relaxation_time: specify a constant relaxation time value
          
          Returns:
              a matplotlib object