Analysis of frequency response of high power MUTC photodiodes based on photocurrent-dependent equivalent circuit model

Abstract

A back-illuminated mesa-structure InGaAs/InP modified uni-traveling-carrier photodiode (MUTC-PD) is fabricated and its frequency response is investigated. A bandwidth of 40 GHz and a saturation photocurrent up to 33 mA are demonstrated. A photocurrent-dependent equivalent circuit model is proposed to analyze the frequency response of the high power MUTC-PDs. The influences of the space-charge screening, self-induced electric field and over-shoot effects are discussed in detail based on the model. Fitted curves obtained from the simple equivalent circuit model are found to be in good agreement with the data measured under different bias voltages and photocurrents.

Accurate equivalent circuit model for millimetre-wave UTC photodiodes

“…4, is a current source which is only active when the device is illuminated, otherwise it is an open as in the case of the S 11 /impedance measurement discussed in this section. In any case, in agreement with [19], we found that, when the DC photocurrent is below the saturation, the circuit parameters do not change with respect to the optical power. If the UTC capacitance was only due to the single capacitance associated with the depletion layer, one should expect the photodiode capacitance to be essentially frequency independent.…”

“…Recently an experimental and circuit analysis up to 40 GHz, of a back-illuminated modified UTC (MUTC), has been presented in [19] in which the authors discuss a new circuit model to fit the measured S 11 and show the agreement between measurement and calculation on Smith Charts. In [19] the new circuit model is employed to study the MUTC dynamic frequency response; the transit time contribution to the photo-response is inferred by fitting the measured photo-response, starting from the RC limited response calculated by means of the circuit parameters obtained by fitting the measured S 11 .…”

High-bandwidth uni-traveling carrier waveguide photodetector on an InP-membrane-on-silicon platform

“…The thickness of the p-InGaAs layer is chosen as a trade-off between the modal absorption coefficient and the transit time of electrons. On the one hand, the thickness assures a sufficient quantum efficiency (> 97%) for a 10 µm PD according to simulations; and on the other hand, it leads to a transit time through the absorption layer (τ a ) of about 1 ps for a pure diffusion transport of electrons [18]. This time constant is comparable to the time constant for electrons drifting through the i-InP layer, as will be discussed later.…”

“…In fact, the electric field through such a thin intrinsic layer is usually above the velocity overshoot regime even with zero bias. In this case, the value of τ c will increase to 3 ps assuming a saturation velocity of 1 × 10 7 [18]. For these two cases, the transit-time limited 3dB bandwidths ( f tr ) are 123 GHz and 85 GHz, respectively, using [6,19] …”

“…Particularly, as there is no diffusion-blocking layer in our UTC-PDs, electrons can diffuse to the p-contact resulting in a drop of the quantum efficiency. The graded doping profile in the p-InGaAs layer results in a quasi-field of several kV/cm, which is just sufficient for a drift motion of electrons in the direction towards the i-InP layer [18]. This is useful for an enhancement of the quantum efficiency in UTC-PDs without diffusion-blocking layers [14].…”