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In this paper, physically-based simulations are carried out to investigate and design uni-traveling carrier photodiode (UTC-PD) for high-power sub-terahertz wave generation at zero- and low-bias operation. The reliability of the physically-based simulation is demonstrated by comparing with our experimental result. Both the bandwidth and RF output p...
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... However, rigorous studies in UTC-PD have found that the output power drops considerably as the bandwidth of the output signal increases, thus limiting the bandwidth to a higher range [17,18]. An ultrafast UTC-PD was demonstrated with a bandwidth of 170 GHz, but the output power is only −11.3 dBm with photocurrent 2 mA under −1 V bias voltage [19]. ...
Modified near-ballistic uni-traveling-carrier photodiodes with improved overall performances were studied theoretically and experimentally. A bandwidth up to 0.2 THz with a 3 dB bandwidth of 136 GHz and large output power of 8.22 dBm (99 GHz) under the ${-}{{2}}\;{\rm{V}}$ − 2 V bias voltage were obtained. The device exhibits good linearity in the photocurrent-optical power curve even at large input optical power, with a responsivity of 0.206 A/W. Physical explanations for the improved performances have been made in detail. The absorption layer and the collector layer were optimized to retain a high built-in electric field around the interface, which not only ensures the smoothness of the band structure but also facilitates the near-ballistic transmission of uni-traveling carriers. The obtained results may find potential applications in future high-speed optical communication chips and high-performance terahertz sources.
... Many modifications such as inserting a highly doped cliff layer and utilizing a uniform-doped collection layer can alleviate the space-charge effect and improve the output power [5][6][7]. For thermal failure, there are two widely adopted solutions: one is the flip-chip bonding of the PD on high thermal conductivity substrates [8,9], and the other is to make the PD work under a zero bias to mitigate the self-heating effect [10][11][12]. However, the zero-bias operation may lead to the exacerbation of the space-charge effect, ultimately resulting in a decrease of the 3 dB bandwidth and RF output power. ...
... In this study, the commercial software Silvaco ATLAS is used to simulate the frequency response (I (ω)) with a large [11,19]. The parameters of InP and In 0.53 Ga 0.47 As in the simulation are shown in Table 1 [20][21][22]. ...
A modified uni-traveling carrier photodiode with an electric field control layer is proposed to achieve high-speed and high-power performance at a lower bias voltage. By inserting the 10 nm p-type InGaAs electric field control layer between the intrinsic absorption layer and space layer, the electric field distribution in the depleted absorption layer and depleted non-absorption layer can be changed. It is beneficial for reducing power consumption and heat generation, meanwhile suppressing the space-charge effect. Compared with the original structure without the electric field control layer, the 3 dB bandwidth of the 20 µm diameter novel structure, to the best of our knowledge, is improved by 27.1% to 37.5 GHz with a reverse bias of 2 V, and the RF output power reaches 23.9 dBm at 30 GHz. In addition, under 8 V bias voltage, the bandwidth reaches 47.3 GHz.
... The unitraveling-carrier photodiode (UTC-PD) is able to operate faster and outputs larger power when the bias voltage is close to zero. [16][17][18][19] Besides the UTC-PD, Kopytko's group proposed modelling theories on the zero biased long wavelength infrared HgCdTe photodiodes. [20,21] Research has also focused on designing photodiodes that consume less or no electrical power and require lower or zero voltage. ...
We propose a new mode of operation when using a photodiode to extract a variable optical signal from a constant (ambient) background. The basic idea of this ‘zero-mode’ of operation is to force the photodiode to operate at either zero current or zero voltage. We present possible implementations of this novel approach and provide the corresponding equivalent circuits while also demonstrating experimentally its performance. The gain and bandwidth of the zero-mode photodetector are measured and simulated, and they show highly agreement. The gain compression effect because of the nonlinearity of the forward bias region is also explored. Comparing to the conventional photoconductive photodetector, the zero-mode photodetector is able to obtain higher AC gain and lower noise. With the same component used in the circuit, the measured input referred root mean square noise of zero-mode photodetector is 4.4mV whereas that of the photoconductive mode photodetector is 96.9mV respectively, showing the feasibility of the zero-mode of operation for measuring the small variable light signal under a high power constant background light.
A high-speed and high-power modified uni-traveling-carrier photodiode (MUTC-PD) is optimized and fabricated. The optimization method takes carrier transport as the core and considers the hole transport time limited bandwidth of the MUTC-PD for the first time. Taking into account the impact of the electron transport time and RC time constant on device performance, the device is simulated and fabricated. In structure epitaxy, it is proposed to use graded doping to fit Gaussian doping to reduce the epitaxial growth error. The measured bandwidth of the MUTC-PD reaches 34 GHz and the RF output power reaches 17.1 dBm with the mesa diameter of
$20~\mu \text{m}$
. In addition, the influence of modulation depth on high-speed and high-power performance is studied.
We propose a monolithic distributed Bragg reflector (DBR) integrated photodiode using a tapered waveguide with InP and polymer cladding layers for achieving a high efficiency bandwidth product. In the proposed photodiode, a DBR mirror is formed at the end of the waveguide, thereby increasing the effective absorption length of the device. Furthermore, to reduce the coupling loss, the InP and polymer cladding layers are formed under and on top of the core layer, respectively. Consequently, the mutual tradeoff between the bandwidth and quantum efficiency of the photodetector could be alleviated.
Herein, we propose a monolithic reflector-integrated waveguide photodetector with optical isolation between photosensitive mesa and N-contact mesa for achieving a high efficiency bandwidth product. In the proposed photodetector, the photosensitive mesa is optically isolated but electrically connected with the N-contact mesa; this is achieved by etching a portion of the core layer to form a groove on each side of the photosensitive mesa, enhancing the binding of the waveguide to optical power. Furthermore, a mesa is formed separate from the N-contact mesa at the end of the waveguide, and the metal film is deposited to act as a mirror, thereby increasing the effective absorption length of the device. Consequently, the mutual tradeoff between the bandwidth and quantum efficiency of the photodetector could be alleviated.
