CN108807567A - A kind of mercury cadmium telluride avalanche diode detector of modulated surface energy band - Google Patents

Abstract

The invention discloses a mercury cadmium telluride avalanche diode detector capable of modulating the surface energy band. By adding an electrode above the passivation layer in the pn junction depletion region, the energy band of the pn junction at the interface between the passivation layer and the mercury cadmium telluride can be modulated. The effect is to make the pn junction at the interface between the passivation layer and mercury cadmium telluride tend to a flat band state, thereby inhibiting surface leakage currents such as recombination and surface tunneling on the surface. The detector has the advantages of modulating the surface energy band of the pn junction region to make it tend to a flat band state, suppressing the surface leakage current so that the diode works in the Geiger mode under a large reverse bias voltage, which is beneficial to solve the problem of tellurium in the conventional structure. When the cadmium mercury avalanche diode device has a reverse bias greater than the avalanche breakdown voltage, there will be a large leakage current on the surface, resulting in thermoelectric breakdown of the photodiode, which limits it to only meet the problem of signal detection in a linear mode.

Description

A HgCdTe avalanche diode detector with adjustable surface energy band

technical field

The invention relates to the mercury cadmium telluride infrared detector technology, in particular to the design and preparation technology of the mercury cadmium telluride avalanche diode detector.

Background technique

HgCdTe avalanche diode detectors have been reported as early as the 1980s. Due to the ionization coefficient characteristics of HgCdTe itself, it can be used to prepare avalanche photodiodes with no excess noise, which will detect weak infrared signals and high It plays a key role in space-time resolution detection and has developed rapidly in recent years, and has become an important direction for the development of the third-generation infrared imaging detectors. Mercury cadmium telluride infrared avalanche photodiode detector can realize high-speed, weak signal and even single-photon detection due to its advantages of high gain-bandwidth product, high signal-to-noise ratio and suitable for linear imaging. It is widely used in observation and atmospheric detection.

There are two working modes of HgCdTe avalanche diodes: linear mode and Geiger mode. In the linear mode, the output current of the diode is proportional to the number ^of photons irradiated ^on it, and the gain has nothing to do with the number of injected photoelectrons. It can be integrated into an infrared focal plane detector to realize photoelectric imaging of weak signals. ^In the Geiger mode, the reverse bias applied to the HgCdTe avalanche diode is greater than the avalanche breakdown voltage, and its output current does not change with the number of incident photons. , can be used in high-speed optical fiber communication systems, and 3D active/passive dual-mode imaging detection technology.

For HgCdTe avalanche diode detectors with conventional structures (Figure 2), due to the influence of fixed charges in the passivation layer, the pn junction at the interface between the passivation layer and HgCdTe is usually not in a flat-band state, and the surface of the device is prone to depletion, Accumulation and inversion, and manifest as energy band bending, and then generate a series of surface-related dark currents, as shown in Figure 3. Moreover, the leakage current on the surface of the pn junction region is far greater than the generation-recombination current, diffusion current, and tunneling current in the space charge region, which is the most important component of the dark current in the HgCdA avalanche diode avalanche device. Therefore, when the reverse bias voltage of the infrared diode avalanche device of this conventional structure is greater than the avalanche breakdown voltage, there will be a large leakage current on the surface, resulting in thermoelectric breakdown of the photodiode. This limits it to only meet the detection of signals amplified in linear mode. In order to achieve a high avalanche gain factor, the dark current of the avalanche diode must be reduced to realize the detection of weak signals or even single photons in the Geiger mode.

Contents of the invention

The purpose of the present invention is to solve the problem of thermoelectric breakdown of the photodiode due to the large leakage current on the surface when the reverse bias voltage of the HgCdT avalanche diode device with the conventional structure is greater than the avalanche breakdown voltage. To meet the problem of signal detection in linear mode, a proposed method that can modulate the surface energy band of the pn junction region to make it tend to a flat band state, suppress the surface leakage current so that the diode works in Geiger mode under large reverse bias of detectors.

Overall structure description: as shown in Figure 1, the chip includes HgCdTe p-region 1, HgCdTe low-doped n ^- region 2, HgCdTe highly-doped n ⁺ region 3, passivation layer 4, pn junction photosensitive element region Electrode 5, p-region common electrode 6 and surface energy band modulation electrode 7; HgCdTe high-doped n ⁺ region 3 and HgCdTe low-doped n ^- region 2 are formed on HgCdTe p-region 1 by conventional doping Cover the passivation layer 4 on the mercury cadmium telluride, respectively open holes on the passivation layer 4 above the pn junction photosensitive element region 5 and the mercury cadmium telluride p region 1 to make the mercury cadmium telluride highly doped n ⁺ region 3 and the pn junction The photosensitive cell area electrode 5 is connected, and the mercury cadmium telluride p-region 1 is connected to the p-region common electrode 6; the surface energy band modulation electrode 7 is prepared on the passivation layer 4, and its position is in the vertical direction of the mercury cadmium telluride low ^- doped n- On the passivation layer 4 on the pn junction depletion region formed by region 2 and HgCdTe p region 1;

Further structural feature description: HgCdTe p-region 1 concentration is 8×10 ¹⁵ cm ^-3 , HgCdTe low-doped n ^- region 2 concentration is 1×10 ¹⁵ cm ^-3 , vertically HgCdTe highly-doped n ⁺ The HgCdTe low-doped n ^- region 2 under the region 3 has a thickness of 3 μm, and the HgCdTe high-doped n ⁺ region 3 has a concentration of 1×10 ¹⁷ cm ^-3 and a thickness of 1 μm. The passivation layer 4 is composed of cadmium telluride and zinc sulfide, first covering cadmium telluride and then covering zinc sulfide. The thickness of cadmium telluride is between 100nm and 200nm, and the thickness of zinc sulfide is between 0nm and 200nm; the pn junction photosensitive element region electrode 5, the p region common electrode 6 and the surface energy band modulation electrode 7 are composed of tin and gold, first covered with tin , then overlay gold. The thickness of tin is between 20nm and 40nm, and the thickness of gold is between 60nm and 120nm.

Working principle: through the surface energy band modulation electrode 7, the energy band structure of the pn junction region on the surface of HgCdTe can be flexibly modulated to make it tend to a flat band, and the effects of surface leakage current such as surface generation-recombination and surface tunneling can be suppressed, which can effectively reduce The influence of the dark current of the avalanche diode and the channel effect of the carrier surface can further increase the reverse breakdown voltage of the avalanche diode and the electric field strength of the junction region under a large reverse bias before the thermoelectric breakdown occurs, greatly increasing the avalanche gain Factor so that the diode works in Geiger mode under large reverse bias.

Beneficial effects of the present invention: Solve the problem that when the reverse bias voltage of a HgCdTe avalanche diode device with a conventional structure is greater than the avalanche breakdown voltage, there will be a large leakage current on the surface, resulting in thermoelectric breakdown of the photodiode, which is limited to the following For the problem of signal detection in linear mode, the surface energy band of the pn junction region is modulated to make it tend to a flat band state, and the surface leakage current is suppressed so that the diode works in Geiger mode under a large reverse bias voltage.

Description of drawings

Figure 1 is a schematic diagram of a HgCdTe avalanche diode detector with adjustable surface energy bands, where 1 is the HgCdTe p-region, 2 is the HgCdTe low-doped n ^- region, and 3 is the HgCdTe highly-doped n ⁺ 4 is the passivation layer, 5 is the electrode of the pn junction photosensitive element area, 6 is the common electrode of the p-region, and 7 is the surface energy band modulation electrode.

Figure 2 is a schematic diagram of a HgCdTe avalanche diode detector with a conventional structure, where 1 is the HgCdTe p-region, 2 is the HgCdTe low-doped n ^- region, 3 is the HgCdTe highly-doped n ⁺ region, and 4 is the passivation layer, 5 is the electrode of the pn junction photosensitive element area, and 6 is the common electrode of the p area.

Fig. 3 is a diagram of the relationship between the dark current induced on the surface of the mercury cadmium telluride n ⁺ -n ^- -p avalanche diode and the p-type surface potential.

Detailed ways

Example 1

1) An n ⁺ -n ^- -p structure is formed on the p-type HgCdTe by conventional doping, the concentration of the HgCdTe p region is 8×10 ¹⁵ cm ^-3 , and the concentration of the n ^- region is 1×10 ¹⁵ cm ^-3 , the thickness of the n ^- region under the longitudinal n ⁺ region is 3 μm, the concentration of the n ⁺ region is 1×10 ¹⁷ cm ^-3 , and the thickness is 1 μm;

2) First grow a 100nm cadmium telluride passivation layer on the surface of mercury cadmium telluride;

3) Corroding the passivation layer with a cadmium telluride etching solution to open passivation holes in the pn junction photosensitive element area and common electrode passivation holes in the p area;

4) 20 nm of tin is grown on the passivation hole and the passivation layer of the pn junction depletion region, and 60 nm of gold is grown.

Example 2

1) An n ⁺ -n ^- -p structure is formed on the p-type HgCdTe by conventional doping, the concentration of the HgCdTe p region is 8×10 ¹⁵ cm ^-3 , and the concentration of the n ^- region is 1×10 ¹⁵ cm ^-3 , the thickness of the n ^- region under the longitudinal n ⁺ region is 3 μm, the concentration of the n ⁺ region is 1×10 ¹⁷ cm ^-3 , and the thickness is 1 μm;

2) On the surface of mercury cadmium telluride, a 150nm cadmium telluride passivation layer is first grown, and then 100nm of zinc sulfide is grown;

3) Corroding the zinc sulfide with hydrochloric acid, corroding the passivation layer with cadmium telluride corrosion solution, and opening the passivation hole in the pn junction photosensitive element area and the common electrode passivation hole in the p area;

4) 30 nm of tin is grown on the passivation hole and the passivation layer of the pn junction depletion region, and 100 nm of gold is grown.

Example 3

1) An n ⁺ -n ^- -p structure is formed on the p-type HgCdTe by conventional doping, the concentration of the HgCdTe p region is 8×10 ¹⁵ cm ^-3 , and the concentration of the n ^- region is 1×10 ¹⁵ cm ^-3 , the thickness of the n ^- region under the longitudinal n ⁺ region is 3 μm, the concentration of the n ⁺ region is 1×10 ¹⁷ cm ^-3 , and the thickness is 1 μm;

2) On the surface of mercury cadmium telluride, a 200nm cadmium telluride passivation layer is first grown, and then 200nm of zinc sulfide is grown;

3) Corroding the zinc sulfide with hydrochloric acid, corroding the passivation layer with cadmium telluride corrosion solution, and opening the passivation hole in the pn junction photosensitive element area and the common electrode passivation hole in the p area;

4) 40 nm of tin is grown on the passivation hole and the passivation layer of the pn junction depletion region, and 120 nm of gold is grown.

Claims (3)

1. a kind of mercury cadmium telluride avalanche diode detector of modulated surface energy band, including the areas mercury cadmium telluride p (1), mercury cadmium telluride low-mix Miscellaneous n^-Area (2), the highly doped n of mercury cadmium telluride⁺Area (3), passivation layer (4), the photosensitive first region electrode (5) of pn-junction, the areas p public electrode (6) and table Face energy band modulator electrode (7), it is characterised in that：

The highly doped n of mercury cadmium telluride is formed by conventional doping in the areas mercury cadmium telluride p (1)⁺Area (3) and the low-doped n of mercury cadmium telluride^-Area (2)； Passivation layer (4) is covered on mercury cadmium telluride, on the passivation layer (4) above the photosensitive first area (5) of pn-junction and the areas mercury cadmium telluride p (1) respectively Trepanning makes the highly doped n of mercury cadmium telluride⁺Area (3) is connected with the photosensitive first region electrode (5) of pn-junction, the areas mercury cadmium telluride p (1) and the areas p public electrode (6) it is connected；Surface energy band modulator electrode (7) is prepared on passivation layer (4), the mercury cadmium telluride of position in vertical direction is low-doped n^-Area (2) and the areas mercury cadmium telluride p (1) are formed by pn-junction depletion region on passivation layer (4)；

The areas mercury cadmium telluride p (1) a concentration of 8 × 10¹⁵cm^-3, the low-doped n of mercury cadmium telluride^-Area (2) a concentration of 1 × 10¹⁵cm^-3, indulge To the highly doped n of mercury cadmium telluride⁺The low-doped n of mercury cadmium telluride under area (3)^-Area (2) thickness is 3 μm, the highly doped n of mercury cadmium telluride⁺Area (3) concentration It is 1 × 10¹⁷cm^-3, thickness is 1 μm.

2. a kind of mercury cadmium telluride avalanche diode detector of modulated surface energy band according to claim 1, feature exist In：The passivation layer (2) is made of cadmium telluride and zinc sulphide, first covers cadmium telluride in cadmium mercury telluride layer (1), then cover vulcanization Zinc, cadmium telluride thickness is between 100nm to 200nm, and zinc sulphide thickness is between 0nm to 200nm.

3. the equipotential HgCdTe infrared focal plane detector of a kind of active area according to claim 1, it is characterised in that： The photosensitive first region electrode (5) of the pn-junction, the areas p public electrode (6) and surface energy band modulator electrode (7) are made of tin and gold, Tin is first covered, then covers gold, tin thickness is between 20nm to 40nm, and golden thickness is between 60nm to 120nm.