HgTe Nanocrystal-Based Photodiode for Extended Short-Wave Infrared Sensing with Optimized Electron Extraction and Injection

Abstract

Thanks to their narrow band gap nature and fairly high carrier mobility, HgTe nanocrystals (NCs) are of utmost interest for optoelectronics beyond the telecom window (λ > 1.55 μm). In particular, they offer an interesting cost-effective alternative to the well-developed InGaAs technology. However, in contrast to PbS, far less work has been dedicated to the integration of this material in photodiodes. In the short-wave infrared region, HgTe NCs have a more p-type character than in the mid-wave infrared region, thus promoting the development of new electron transport layers with an optimized band alignment. As for perovskites, HgTe NCs present a fairly deep band gap with respect to vacuum. Thus, we were motivated by the strategy developed for perovskite solar cells, for which SnO2 has led to the best performing devices. Here, we explore the following stack made of SnO2/HgTe/Ag2Te, in which the SnO2 and Ag2Te layers behave as electron and hole extractors, respectively. Using X-ray photoemission, we show that SnO2 presents a nearly optimal band alignment with HgTe to efficiently filter the hole dark current while letting the photoelectrons flow. The obtained I–V curve exhibits an increased rectifying behavior, and the diode stack presents a high internal efficiency for the diode (above 60%) and an external quantum efficiency that is mostly limited by the absorption magnitude. Furthermore, we tackle a crucial challenge for the transfer of such a diode onto readout circuits, which prevents back-side illumination. We also demonstrate that the diode stack is reversible with a partially transparent conducting electrode on the top, while preserving the device’s responsivity. Finally, we show that such a SnO2 layer is also beneficial for electron injection and leads to an enhanced electroluminescence signal as the diode is operated under forward bias. This work is an essential step toward the design of a focal plane array with a HgTe NC-based photodiode.

Ultrafast Charge Carrier Dynamics and Transport Characteristics in HgTe Quantum Dots

“…While the field of HgTe quantum dot (QD) colloidal chemistry that started back in the 90s in Horst Weller’s group , is well developed nowadays and has come to provide synthetic recipes for a wide range of QD sizes and thus tunable emission wavelengths up to the mid-infrared (IR) range, − the research focus has shifted more toward IR-device engineering aspects. Various approaches have been implemented to obtain high-performance optoelectronic devices, such as coupling with plasmonic structures, − ligand engineering, surface chemistry control, , a more sophisticated development of the architecture of the device itself, − and so on. During the past 20 years the field of IR optoelectronic devices based on HgX (X = S, Se, Te) colloidal QDs has experienced impressive developments. , Up to date photodetectors with a responsivity up to 10 6 A/W and detectivity of 10 12 Jones beyond 2 μm have been reported. ,, Recently, by combining HgTe QDs and graphene, the sensitivity of phototransistors was greatly improved at wavelengths up to 3 μm .…”

Inside a nanocrystal-based photodiode using photoemission microscopy

“…1e. For SWIR detection, Gréboval et al 27 have proposed the use of a diode stack in which the HgTe NCs are sandwiched between SnO 2 and Ag 2 Te, acting respectively, as electron and hole transport layers, see Fig. 1d.…”

“…Ackerman et al 24 were the first to propose the coupling of an HgTe NC layer with an Ag 2 Te layer, the latter being used as a hole extraction layer. Since then, many derivatives have been considered, in particular through the addition of an electron transport layer (Bi 2 S 3 , 25 CdSe, 26 SnO 2 27 ), confirming the potential of this specific diode stack for HgTe NC-based infrared sensing. To move beyond the already explored structures while avoiding an inefficient trial-and-error approach, deeper knowledge of the electronic structure must be correlated with the development of new diode stacks.…”

Mercury chalcogenide colloidal quantum dots for infrared photodetection: from synthesis to device applications

“…A rectification ratio of up to 2000 and a record low dark current of 2.3 × 10 −6 A cm −2 under −0.4 V reverse bias were achieved, resulting in a high LDR of over 112 dB at 1.55 µm. Other alternative ETLs were also explored with doped SnO 2 146 and CdSe QD 147 layers, with the optimal band alignment of HgTe QDs to improve the electron extraction and block the hole current. An inverted diode structure was also demonstrated with a stack of doped-SnO 2 /HgTe QDs/Ag 2 Te QDs, which was compatible with ROIC integration, with a top illumination scheme (Fig.…”