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 /spl mu/m depleted InP cap region, together with 1 /spl mu/m depleted InGaAs absorption region and 0.3 /spl mu/m depleted InP buffer region, having the capacitance as small as those devices with 1.6 /spl mu/m depletion region, while have the carrier transit time as short as those devices with 1.3 /spl mu/m depletion region. Under appropriate bias condition, which is required for getting rid of the heterointerface effects, the symmetrical device as stated with 40 /spl mu/m 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 /spl sim/0.1 /spl mu/m 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 /spl sim/0.8 A/W at -5 V at 1.3 /spl mu/m 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.