A Optical response of In_xGa_1-xAs pin detector

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The discussion focuses on the photocurrent response of a GaAs/InGaAs/Si top-illuminated pin photodetector with varying compositions of In_xGa_1-xAs. The user expects specific peak wavelengths based on the energy bandgap (Eg) values for different x concentrations, but notices that the expected peaks disappear for higher x values (0.2 and 0.3). The user seeks a physical explanation for this phenomenon, particularly why the expected photocurrent peaks do not align with the theoretical predictions. The conversation highlights the complexities of the active layer's behavior in relation to doping concentrations and material properties. Understanding these interactions is crucial for optimizing the performance of the photodetector.
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Plot of the photocurrent versus the wavelength of light of a GaAs/InGaAs/Si top-illuminated pin photodetector
Greetings,

I am trying to obtain a plot of the photocurrent versus the wavelength of light of a GaAs/InGaAs/Si top-illuminated pin photodetector, where the doping ratio for p-type GaAs is conc=1e17, for i-layer In_xGa_1-xAs conc=1e14 and for n-type Si conc=1e18. Firstly, for x=0.05, if we illuminate this structure with top light, the plot of the photocurrent versus the wavelength of light we obtain is as follows:
1726818041237.png


For x=0.1:

1726818141092.png


For x=0.2:

1726818158378.png


Finally, for x=0.3:

1726818194029.png


What I don't fully understand here is that the In_xGa_1-xAs layer is the active layer here and Eg=1.351 eV for x=0.05, so I would expect a peak of around 0.918 micrometres in the wavelength plot of the current coming out of the pin detector. The same situation is Eg=1.279 eV for x=0.1 and the corresponding cut-off wavelength is a peak at 0.970 micrometres. Moreover, for x=0.2 and 0.3 the peak disappears as you can see in the graphs. What could be the physical explanation for these phenomena?
 

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