Help to plot the LED Characteristic Curve

I am trying to plot the LED characteristic curve, but I am not getting the correct curve.The theoretical curve is below.

The curve I'm finding is this. A little different than expected.

Someone could help me with what I'm wrong. I'm submitting my code below.

% LED information
Vt = 0.5; 
Is = 0.5; 

% LED model
K = 0.5; 
imax = 0.5; 
threshold = 150;
sigmaV2 = (imax./threshold).^2;

% number of bits
L = 1e4;

SNRdB = 40;

% Signal-to-Noise Ratio Lin.
SNR = 10.^(SNRdB/10); 
r = 10.^(SNRdB/10);

% signal standard deviation (power)
sigmaX2v = SNR.*sigmaV2;

% Maximum number of iterations for a single SNR
max_run = 100;


for sk = 1:length(SNRdB)
    
    for tk = 1:max_run
        s = linspace(0,100,10000); % input
        s1 = s.';
        stdS = std(s1);
        X = zeros(1,4.*L);
        X(2:2:end) = [s1; conj(s1(end:-1:1))]; 
        xTD = ifft(X);
        xTD = (sqrt(sigmaX2v(sk))).*xTD./std(xTD);
        xx = xTD;
        ind = find(xTD < 0);
        xx(ind) = zeros(size(ind));
        ss = xx;        

        iLED = Is.*(exp(ss./Vt) - 1); 
        xLED = iLED./((1 + (iLED./imax).^(2.*K)).^(1./(2.*K))); 
        
        y = xLED; 
        
        Nframe = length(y);
        Xhat = (fft(y)+10);
        Shat = Xhat(2:2:Nframe/2);
        Shat = stdS.*Shat./std(Shat); 
        Y = Shat; % output

    end
end


plot(s1,Y)

Answer 1

[Sulaymon Eshkabilov]

The answer in signal-to-noise ratio value, e.g:

SNRdB = 20;  % Gives a nice looking one!

[adriane duarte]

could you tell me if my curve would be right?

[Sulaymon Eshkabilov]

Your obtain curve shape changes because of the SNR value. Thus, whichever value is your actual value for simulation that would be appropriate. You can simulate your code with different values of SNR and see how SNR inluences your curve shape.

[adriane duarte]

I found my curve in the figure above very strange because it grows back from a certain point. I thought the LED curve couldn't happen.