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Emission: Internal Quantum Efficiency

In this tutorial we demonstrate how to calculate the internal quantum efficiency of a multi-quantum well structure as a function of the applied forward bias.

Physics Model

nextnano++ is capable of simulating recombination processes such as Shockley-Read-Hall (SRH), Auger and radiative recombination. Only the radiative (direct) recombination process (spontaneous emission) generates photons. If radiative recombination $R_{\rm sp}(x)$ is summed up over the full device, it equals the total number of photons emitted from the device per second, the photocurrent: $I_{\rm photon}$.

$$R_{\rm sp}= c_r (n p- n_{\rm i}^2)$$

$$I_{\rm photon} = \int\limits_{V_0} R_{\rm sp} {\rm d}V$$

If the injected charge carrier current is $I_{\rm charge}$, then the internal quantum efficiency $\eta_{\rm qe}$ is

$$\eta_{\rm qe} = \frac{I_{\rm photon}}{I_{\rm charge}}$$

Input file structure

Drift Diffusion

      SRH            = yes       # Shockley-Read-Hall recombination
      Auger          = yes       # Auger recombination
      radiative      = yes       # radiative recombination (direct recombination)

The internal quantum efficiency is calculated automatically when the radiative recombination is switched on

     radiative      = yes       # radiative recombination (direct recombination)



The band structure of the MQW structure can be seen in figure 1 without bias voltage.

Figure 1: Band structure at zero bias. The two quantum wells consist of ${\rm In}_{0.7}{\rm Ga}_{0.3}{\rm As}$ and are surrounded by ${\rm In}_{0.53}{\rm Ga}_{0.47}{\rm As}$ barriers.


An example for the distribution of the recombination processes is plotted in figure 2

Figure 2: Comparison of different recombination processes. The applied bias is 1 V.

Current-Voltage Characteristics

The $I-V$ characteristics of the device is plotted in figure 3. This figure also includes the full photo current.

Figure 3: $I-V$ characteristics of the device and photo current. The device has two contacts and the charge carrier current densities at the left and at the right contact are equal in absolute value.

Quantum Efficiency

The internal quantum efficiency is plotted in figure 4

Figure 4: Internal quantum efficiency as a function of the forward bias voltage

nnp/optics/internal_quantum_efficiency.txt · Last modified: 2017/02/03 10:19 by stefan.birner