Short-wave infrared HgCdTe focal plane array for astronomical K-band observation

ObjectiveInfrared astronomical observation serves as a vital technical means for exploring the universe. The short-wave infrared band, which bridges the visible and mid-infrared ranges, carries extremely rich spectral information from the cosmos and constitutes an indispensable window for astrophysical research. Unlike conventional Earth observation, the extreme faintness of astronomical targets demands detectors with extremely low dark current and readout noise. Due to a relatively late start and the early lack of major astronomical project drivers, progress in the development of astronomical infrared detectors in China has been relatively slow, with device performance primarily limited by dark current and readout noise. In recent years, with the advancement of major national projects such as the Chinese Space Station Telescope, the demand for domestically produced astronomical infrared detectors has grown increasingly urgent. Therefore, this paper conducts a study on the short-wave HgCdTe infrared focal plane array used for astronomical observations.MethodsThe HgCdTe material was grown using liquid-phase epitaxy, and the device employs an n-on-p structure (as shown in Fig.1). P-type doping of the material was achieved through high-temperature annealing, while n-type doping was realized via boron ion implantation to form the p-n junction. A gradient passivation layer with high Cd composition was formed on the device surface to suppress surface leakage current. The device was interconnected with a designed readout integrated circuit (ROIC) via flip-chip bonding, resulting in a focal plane array with a format of 640×512 and a pixel pitch of 15 μm. The detector was systematically characterized at liquid nitrogen temperature using the photon transfer curve (PTC) method. Figure 2 shows a schematic diagram of the infrared focal plane array test system used in this study.Results and DiscussionsAt liquid nitrogen temperature, the detector exhibits a dark current of 4.7 e−/s·pixel−1 (Fig.5), representing a reduction of over an order of magnitude compared to the level before device fabrication process optimization. The readout noise is 65 e− (Fig.7), and the cutoff wavelength is 2.8 μm (Fig.8). The quantum efficiency in the K-band reaches 85%, which is comparable to reported values for astronomical short-wave infrared detectors. The full-well capacity is 97 340 e− and the effective pixel operability is 99.4% (Fig.11). Field observation results indicate that the detector achieves an observation sensitivity of 15.1 mag with an integration time of 20 s. The sensitivity of the detector is primarily limited by sky background noise, the detector's own readout noise and dark current are not the bottleneck for the overall observational performance of the telescope.ConclusionsIn this paper, we report a short-wave infrared focal plane with a 640 pixel×512 pixel array format, 15 μm pixel pitch. The device was fabricated based on liquid-phase epitaxial HgCdTe material. Dark current was suppressed by forming a high-Cd-composition passivation layer on the device surface and optimizing the power consumption of the readout circuit. When operated at liquid nitrogen temperature, the detector demonstrates a cutoff wavelength of 2.8 μm, a dark current of 4.7 e−/s·pixel−1, a readout noise of 65 e−, a K-band quantum efficiency of 85%, a full-well capacity of 97 340 e−, and an effective pixel operability of 99.4%. Field observation results indicate that the detector achieves an observation sensitivity of 15.1 mag with an integration time of 20 s. These results demonstrate that the detector's performance meets the requirements for ground-based astronomical K-band observations. Future work will initially focus on optimizing the detector's readout noise. In addition, given that the mainstream international astronomical HgCdTe infrared focal plane array is currently based on the p-on-n structure, parallel research on p-on-n short-wave HgCdTe infrared focal plane array will also be carried out to explore methods for further reducing dark current. On this basis, research on larger-format astronomical infrared focal plane array will be conducted.