InGaN ternary alloys with their band gaps varying from 0.7 to 3.4 eV, are very promising for photodetector devices operating from UV to IR wavelength range. Using Silvaco–Atlas software, an In0.1Ga0.9N/GaN based p–i–n photodiode is designed and theJ–Vcharacteristics, the spectral responsivity, the frequency response and the cut‐off frequency as a function of InGaN thickness are studied. The photodiode exhibits a high reverse breakdown voltage of 38 V, a peak responsivity of 0.2 A W−1at 0.343 μm wavelength and a cutoff frequency of 400 MHz under an applied reverse bias voltage of 2 V and for a 0.1 μm i‐InGaN layer, in good agreement with simulated and experimental results found in literature. It is found that an optimum i‐layer thickness of 1.5 μm for the maximum cutoff frequency of 4 GHz attributed to the predominance of the limitation in capacitance effect on the cutoff frequency at low i‐layer thickness and the transit time on the cuttoff frequency for high i‐layer thickness. For this i‐layer thickness, the highest peak responsivity about 0.244 A W−1at 0.384 μm wavelength is achieved.