Research on Au-doped Mercury Cadmium Telluride long-wavelength detector based on Kunming Institute of Physics

According to Mams Consulting, the scientific research team of the Kunming Institute of Physics recently published an article on the theme of "Research on Au-doped Mercury Cadmium Telluride Long Wave Detector Technology" in the journal "Infrared and Laser Engineering". The corresponding author of this article is Senior Engineer Kong Jinchengzheng, who is mainly engaged in the research of infrared materials and devices. The first author of the article is senior engineer Song Linwei, who is mainly engaged in research on infrared materials and devices.

This article is based on the Kunming Institute of Physics' Au-doped mercury cadmium telluride material stability control and device dark current control technologies, and reports on the development progress of extrinsic Au-doped long-wavelength mercury cadmium telluride devices at the Kunming Institute of Physics.

Parameter control of Au-doped mercury cadmium telluride long-wavelength materials

Since Au doping atoms are fast-diffusing impurities in mercury cadmium telluride materials, they can easily diffuse and enrich into defect areas and interfaces during heat treatment and processing. Therefore, in the Au doping device process, the Au doping material needs to be controlled first. stability. Since there will be a large number of mercury vacancies (VHg) in the mercury cadmium telluride film grown by Te-rich liquid phase epitaxial growth, the doped Au atoms can easily occupy the mercury lattice site to achieve acceptor doping under this condition, and higher doping can be achieved. For the growth of concentration materials, the Kunming Institute of Physics uses Te-rich horizontal liquid phase epitaxy technology to achieve the growth of Au-doped long-wave materials with controllable doping concentration.

After the epitaxial growth of the Au-doped mercury cadmium telluride material, there are many mercury vacancies in the material. Therefore, the raw material at this time shows a high concentration of P-type, with mercury vacancies playing a dominant role. The Au-doped raw material needs to be subjected to mercury saturation heat treatment. , to fill the mercury vacancies in the material, so that the Au doping atoms in the material dominate, showing P-type conductivity. However, Au doping atoms are fast-diffusing impurities. During the heat treatment process, they tend to diffuse and enrich toward the interface and defects. The concentration of Au doping atoms inside the material decreases. The fast diffusion characteristics of Au doping atoms make the electrical parameters of the material uncontrollable after heat treatment. It seriously affects the yield of epitaxial materials and the stability of subsequent processes.

Regarding the stability control problem of Au-doped mercury cadmium telluride materials caused by the fast diffusion characteristics of Au atoms, the study found that introducing a certain mercury vacancy during heat treatment can help improve the stability of Au doped atoms, thereby improving the electrical properties of Au materials mercury cadmium telluride materials. Parameter control. When preparing P-type materials, the Au doping concentration can be stably controlled between 1.0×10¹⁶~4.0×10¹⁶cm⁻³. After heat treatment, the carrier concentration of the mercury cadmium telluride epitaxial material can be basically controlled between 1.0×10¹⁶~4.0×10¹⁶cm⁻³. The preparation of Au-doped mercury cadmium telluride long-wavelength materials with good stability was achieved.

Dark current of Au-doped n-on-p mercury cadmium telluride long-wavelength detector

The device dark current is a characteristic parameter that reflects the nature of the detector, and the size of the dark current determines the device performance. Among various dark currents in mercury cadmium telluride devices, diffusion current and generation-recombination current are determined by the electrical properties and recombination mechanism of the material, while tunneling current is related to material defect properties. Diffusion current is a current formed by the diffusion and drift of carriers at both ends of the space charge region of a PN junction under the action of an electric field. It is a current formed by carriers within the minority carrier diffusion length at both ends of the space charge region under thermal equilibrium.

When the carrier concentration is the same, the diffusion current of a mercury cadmium telluride device is inversely proportional to the minority carrier lifetime. Therefore, increasing the minority carrier lifetime of the material can reduce the device diffusion current. The use of extrinsic Au doping atoms to replace intrinsic mercury vacancies, which are deep level recombination centers, helps reduce deep level defects in mercury cadmium telluride materials, improve the minority carrier lifetime of P-type mercury cadmium telluride materials, and reduce device darkness. current, thereby achieving the purpose of improving the performance of n-on-p type devices.

The Kunming Institute of Physics uses Au doping technology to prepare Au-doped long-wave mercury cadmium telluride (10.5μm@80K) materials with a carrier concentration of 1.5×10¹⁶cm⁻³. The minority carrier lifetime reaches 0.25μs, which is the same technology as currently reported. The highest level of route material minority carrier life span is equivalent.

Figure 1 shows the dark current comparison of the extrinsic Au doping technology and the intrinsic mercury vacancy type long-wavelength 256×256 (30μm) mercury cadmium telluride focal plane device. The dark current of the long-wavelength 256×256 mercury cadmium telluride device with a cut-off wavelength of 10.6 μm at 80K is 1980 pA, while the dark current of the extrinsic Au-doped device with a cut-off wavelength of 10.5 μm at the same temperature is only 171 pA, using Au doping. The technology can effectively reduce the dark current of n-on-p long-wave focal plane devices. The dark current density of long-wave devices is reduced from 2.2×10⁻⁴A·cm⁻² to 1.9×10⁻⁵A·cm⁻², and R₀A is reduced from 31.3Ω. cm² increased to 363Ω·cm².

Figure 1 a) Comparison of dark current distribution between intrinsic mercury vacancy n-on-p type devices and; b) extrinsic Au doped devices

Figure 2 shows the dark current changes with operating temperature of the Au-doped long-wavelength device prepared by Kunming Institute of Physics. The upper and lower trend lines are the theoretical dark current control values ​​of n-on-p devices and p-on-n devices respectively. Comparison shows that the dark current level of extrinsic Au-doped devices is significantly lower than that of intrinsic mercury vacancies n-on-p. type devices, and as the operating temperature increases, the dark current of Au-doped long-wave devices is closer to the theoretical value of Rule07 p-on-n-type devices. At 110K, the dark current control of Au-doped long-wave devices is consistent with Rule07 p-on-n The device control level is close.

Figure 2 Dark current changes with temperature in Au-doped long-wavelength mercury cadmium telluride device

Figure 3 is a comparison chart of the dark current control level of Au-doped long-wave devices of Kunming Institute of Physics and the international advanced level. The R₀A value of Au-doped long-wave devices is at least one order of magnitude higher than that of conventional mercury vacancy n-on-p-type devices, and is the same as that of p- The R₀A value control level of on-n-type devices is close to that of Kunming Institute of Physics. The dark current control of Au-doped long-wavelength devices of Kunming Institute of Physics is close to the international advanced level, laying the foundation for the development of high-performance long-wavelength focal plane devices.

Figure 3 Dark current control level of Au-doped long-wavelength devices

Au doped mercury cadmium telluride long wave detector

Based on the advantages of Au doping technology in dark current control of mercury cadmium telluride devices, the Kunming Institute of Physics has successively developed Au-doped mercury cadmium telluride 256×256 (30 μm), 640×512 (25 μm), and 640×512 (15 μm). ) and other specifications and models (as shown in Figure 4 to Figure 7), the performance is equivalent to the device level reported abroad, realizing the serial development of extrinsic Au-doped long-wave mercury cadmium telluride devices and achieving mass production level. Typical performance indicators of several devices are shown in Table 1.

Figure 4 Long-wavelength 256×256 (30μm pitch) detector: a) physical component diagram; b) response signal diagram; c) NETD histogram

Figure 5 Long-wavelength 640×512 (25μm pitch) detector: a) physical component diagram; b) response signal diagram; c) NETD histogram

Figure 6 Long-wavelength 640×512 (15μm pitch) detector: a) physical component diagram; b) response signal diagram; c) NETD histogram

Figure 7 Long-wavelength 1024×768 (10μm pitch) detector: a) physical component diagram; b) response signal diagram; c) NETD histogram

Long-term stability of Au-doped mercury cadmium telluride detectors

In previous research, the French company Sofradir believed that since Au atoms are fast-diffusing impurity atoms, they may have a certain impact on the long-term stability of the device. In response to this problem, the Kunming Institute of Physics has carried out research on the stability of Au-doped mercury cadmium telluride devices in high and low temperature storage, high and low temperature cycles (+70°C ~ -40°C) and long-term storage. There is no significant change in device performance after low temperature cycling. Figure 8 shows the changes in NETD and blind elements of the Au-doped mercury cadmium telluride long-wavelength 256×256 device over storage time. After the package was packaged in 2015, it has been stored at room temperature for more than 7 years, and during the storage period it is about 6 Performance tests were conducted at monthly intervals, and the test data showed that the device performance of the Au-doped device did not change significantly during long-term storage for 7 years.