Bandwidth enhancement for p-end-illuminated InP/InGaAs/InP p-i-n photodiodes by utilizing symmetrical doping profiles

This paper shows that the bandwidth of a p-end-illuminated planar InP-InGaAs-InP heterojunction p-i-n photodiode can be promoted by using a rather symmetrical doping profile that is produced through diffusion depth control. Caused by extra-depleted InP region in the end of p-InP, the device with symmetrical doping profile has additional series capacitance and thus has a smaller total capacitance than conventional asymmetrical doping profile. Such devices with 0.3 μm depleted InP cap region, together with 1 μm depleted InGaAs absorption region and 0.3 μm depleted InP buffer region, having the capacitance as small as those devices with 1.6 μm depletion region, while have the carrier transit time as short as those devices with 1.3 μm depletion region. Under appropriate bias condition, which is required for getting rid of the heterointerface effects, the symmetrical device as stated with 40 μm junction diameter can have a 3 dB bandwidth exceeding 17 GHz without inductance optimization. For device with conventional asymmetrical doping profile, that is, the p-n junction locating at ~0.1 μm deep in the InGaAs layer, only a bandwidth of about 15 GHz can be obtained. Due to the same thickness of InGaAs absorption layer, both devices have similar responsivity of ~0.8 A/W at -5 V at 1.3 μm wavelength. However, the heterointerface exposed in the depletion region results in several detrimental effects in symmetrical devices, such as interface-generation current, which leads to slightly increased dark current, and barrier/traps for hole transport, which lead to inferior photoresponse at low biases