WO2016015077A1

WO2016015077A1 - Optoelectronic infrared sensor

Info

Publication number: WO2016015077A1
Application number: PCT/AT2015/050182
Authority: WO
Inventors: Niyazi Serdar Sariciftci; Vedran DEREK; Eric Daniel GLOWACKI; Mile IVANDA
Original assignee: Universität Linz
Priority date: 2014-07-29
Filing date: 2015-07-28
Publication date: 2016-02-04
Also published as: AT516109A1

Abstract

Disclosed is an optoelectronic infrared sensor comprising two semiconductor layers, a p-doped silicon layer (1) and an organic semiconductor layer (2) on the silicon layer (1), each layer being connected to one electrode (3, 4) and the two layers forming a heterojunction. In order to achieve advantageous design conditions, the organic semiconductor layer (2) is provided on a nanostructured and/or microstructured surface layer (6) of the silicon layer (1) and covers the entire area of said surface layer.

Description

Optoelectronic infrared sensor

Technical area

The invention relates to an optoelectronic infrared sensor with two each connected to an electrode, a heterojunction forming semiconductor layers, namely a silicon layer and an organic semiconductor layer on the silicon layer.

State of the art

Infrared sensors are major components in many optoelectronic devices used in telecommunications, sensor technology and image technology. Near-infrared sensors are commonly fabricated using low-band-gap semiconductors, with indium gallium arsenide prevalent in most applications, although the toxicity of the starting materials and integration into silicon-based microelectronics leads to difficulties. Silicon-based near-infrared sensors would therefore represent an advantageous alternative to infrared indium gallium arsenide sensors. Many attempts have therefore been made to provide near-infrared sensors based on silicon, but the known infrared sensors of this type could not compete with the sensors based on indium gallium arsenide due to various disadvantages.

For example, optoelectronic infrared sensors are known (WO

09/023881 A1), which have an inorganic semiconductor layer forming a heterojunction with an organic semiconductor layer, wherein the inorganic semiconductor layer preferably consists of a p-doped silicon layer which, with a semiconductor layer based on a fullerene, forms the heterojunction forms. A disadvantage of these known infrared sensors, however, is that the two semiconductor layers must be cooled. With increasing cooling, the photocurrent based on absorption of the infrared radiation increases and can be used to detect infrared radiation. Infrared sensors for the near infrared range have also been proposed (Mateusz Bednorz, Gebhard J. Matt, Eric D. Glowacki, Thomas Fromherz, Christoph J. Brabec, Markus C. Scharber, Helmut Sitter, N. Serdar Sariciftci: Silicon / organic hybrid heterojunction infrared photodetector operating in the telecom regime; Organic Electronics, Volume 14, May 12013, pp. 1344-1350), which rely on a heterojunction between a p-type silicon semiconductor layer and an organic semiconductor based on a perylene derivative, and a photovoltaic effect show up to 2.7 μιη (0.46 eV), that is, a value that is significantly lower than the band gap of the two semiconductor materials. Nevertheless, the sensitivity remains too low for industrial use.

Finally, in a solar cell for energy conversion without reference to an infrared sensor, it is known (Xiaojuan Shen et al .: Hybrid Heterojunction Solar Cell Based on Organic-Inorganic Silicon Nanowire Array Architecture, J. Am. Chem. Soc, 201 1, 133 (48) , pp 19408-19415) to form the silicon semiconductor layer by a metal-assisted, wet-chemical etching process of the planar surface with a nanowire field, which is covered by a thin organic semiconductor layer. The achievable increase in performance depends in particular on the structure of the nanowire field and the upper contact points between the nanowire field and the organic semiconductor layer and is attributed on the one hand to the scattered by the wire structure light scattering and thereby improved light absorption and on the other hand to the new contact points. However, low charge carrier mobility and thus overall poor electrical properties result.

Presentation of the invention The invention is thus based on the object, an optoelectronic infrared sensor with a heterojunction between a silicon layer and an organic semiconductor layer in such a way that a high sensitivity for a caused by a near infrared radiation photocurrent can be ensured without having to make a cooling of the semiconductor layers.

Starting from an optoelectronic infrared sensor of the type described above, the invention achieves the stated object in that the organic semiconductor layer is provided on a nanostructured and / or microstructured surface layer of the silicon layer and covers it over its entire area. Although the heterojunction resulting boundary layer between the inorganic and organic semiconductor layers is increased by the nano- and / or microstructure of the silicon layer accommodating the organic semiconductor layer, this interfacial increase can be compared to the detectable increase in the sensitivity of an infrared sensor according to the invention by ten to five hundred times to known infrared sensors with a un-structured interface between the inorganic and organic semiconductor layers and the functionality of the infrared sensors according to the invention also at room temperature do not explain, especially since these effects are not observed in an n-doped silicon layer. On the contrary, it has been shown that the light absorption in the near infrared range between 2 and 1.2 μm by the structured silicon layer is even lower by 1 to 5% compared to a planar silicon layer, which, in contrast to the noticeable, extraordinary increase in the Photocurrent current is on average a hundredfold. Although an explanation of the surprising effect of the inventive measures depends primarily on a satisfactory understanding of the charge carrier excitation in the heterojunction between the p-doped silicon and the organic semiconductor, it is currently assumed that the change in the electric field strength caused by the structuring of the silicon layer in the area of the structure-related edges and peaks of the heterojunction plays a decisive influence. presuppose For this purpose, the organic semiconductor layer is the structured surface of the silicon layer while maintaining a largely constant

Layer thickness covers the entire surface, so the nano- or microstructuring of the silicon layer largely follows. With the signal-to-noise ratio, which is sustainably increased even without cooling, advantageous prerequisites are created for adapting the infrared sensors according to the invention to different applications because organic semiconductor materials having different properties can be used for this without having to fear that the sensitivity drops to an insufficient level for technical applications ,

Suitable organic semiconductor layers are molecular or polymeric organic semiconductors, the polarity of their majority charge carriers having to be negative. Preferred semiconductor materials are organic molecules which have good stability due to hydrogen bonds. Due to the chemical and operational stability of such organic semiconductors given by the hydrogen bonds, the prerequisite for many different applications is created.

The structural formulas of such different organic semiconductor materials are given below, which can be advantageously used in infrared sensors according to the invention, wherein

R 1, R 2 is H, an alkyl, alkoxyl, aryl or an aryloxyl group,

R ₃ , R _{4 is} a halogen, an alkyl or alkoxy group or an aromatic

Group, such as phenyl or thienyl, stand and

R ₅ indicates an alkyl or alkoxy group or an aromatic group such as phenyl or thienyl substituent.

(1 )

i7)

125 (8)

(9)

(12)

135 (13)

The given structural formulas (1) to (16) show that different, very stable molecules, in particular of the Indigo family, can be used in order to be able to take into account a wide variety of applications with the aid of the different organic semiconductors. However, the invention is not limited to the use of these semiconductor materials.

For the silicon layer, a p-doped, momokristallines, but also polycrystalline silicon can be used. The nanostructure of the surface layer of the silicon layer can be produced by a chemical or electrochemical etching process in a manner known per se. Microstructures can be obtained by expanding the pores of a nanostructure by a subsequent chemical etching step or the formation of micropyramids by means of anisotropic etching. Particularly favorable conditions for structuring can be achieved when using a silicon having a <100> or a <1 1 1> orientation, because the etching processes are carried out using appropriate etching methods <1 1 1> crystal facets of silicon are selectively released to form a pyramidal pattern. Decisive in the structuring of the surface layer of the silicon is that edges, tips and / or corners are formed by the selected structuring, which cause an increase in the electric field strength, as is the case in particular with micropyramids. The depth of structuring can range between a few nm to a few μιη. Brief description of the drawings

In the drawing, the subject invention is shown, for example. Show it

Fig. 1 an optoelectronic infrared sensor according to the invention in one

schematic cross section,

FIG. 2 shows the silicon layer with a nanostructured surface layer receiving the organic semiconductor layer and FIG

3 and 4 show the current density profile versus the voltage of various infrared sensors according to the invention in comparison to corresponding infrared sensors without a structured surface of the silicon semiconductor layer. Way to carry out the invention

As can be seen from FIG. 1, the optoelectronic infrared sensor forms a photodiode, which is composed of an inorganic semiconductor layer formed by a p-doped silicon layer 1 and an organic semiconductor layer 2 applied to this silicon layer 1 to form a heterojunction the silicon layer 1 and the organic semiconductor layer 2 are each connected to an electrode 3, 4, for example of vapor-deposited aluminum. The exposure of the photodiode with a near infrared radiation 5 takes place from the side of the silicon layer 1. This means that the silicon layer 1 acts as a filter for the exciting radiation, so that due to the size of the band gap of the silicon, the radiation range only up to about 1, 1 eV can be used. At the bottom, the detectable radiation is limited by the electronic structure formed by the boundary layer between the silicon layer 1 and the organic semiconductor layer 2 used in each case. In contrast to known infrared sensors of this type, the silicon layer 1 is provided with a nano- and / or microstructured surface layer 6, as indicated in FIG. Such a pore structure can be achieved for example by an electrochemical etching of the monocrystalline silicon layer by known methods. However, other known methods for surface structuring can also be used, as the following examples show.

example 1

A p-doped, monocrystalline, <100> -oriented silicon with a carrier density in the range of 10 ¹³ to 10 ¹⁵ cm ^"3 is used as a substrate, wherein an electrode preferably made of aluminum on one side of the silicon substrate is applied so that The silicon substrate is provided with a nanostructured surface layer in the form of pores formed by electrochemical anodization in 48% hydrofluoric acid The silicon substrate was vacuum heated to 580 ° C. by flashlamp annealing and then cooled to 70 ° C. An organic semiconductor layer of 6,6'-dibromindigo in a thickness of 20 to 40 nm was applied to the silicon substrate prefabricated in this manner a hot wall epitaxial process to form a conformal coating of the structure to reach the silicon layer. An electrode made of aluminum, the size of which determines the active area of the infrared sensor, is then deposited on the organic semiconductor layer. The responsiveness of such an infrared sensor begins at 2700 μιη.

FIG. 3 shows the current density profile versus an infrared sensor with a comparable heterojunction, but without nanostructuring Surface of the silicon layer clearly. On the abscissa the voltage in V and on the ordinate the current density in mA / cm ^{2 is} plotted on a logarithmic scale. The current density profile 7 of the infrared sensor according to Example 1 is shown with a full thicker line compared to the current density profile 8 of the unstructured comparative example. The infrared radiation was in each case with 40 mW / cm ² at a wavelength of 1, 48 μιη.

Example 2

In contrast to example 1, the p-doped silicon substrate with a <100> crystal orientation is not subjected to an electrochemical anodization in hydrofluoric acid, but to anisotropic etching using a KOH-isopropanol-water mixture, to give micropyramides with a high content at the surface to produce facing <1 1 1> facets. After drying and cleaning by known methods, the silicon substrate is vacuum heated to 580 ° C by flash-annealing and then cooled to 70 ° C before the substrate of Example 1 with an organic semiconductor layer of 6,6'-dibromoindigo in thickness between 20 and 40 nm is coated. The infrared sensor manufactured in this way has a response sensitivity beginning at 2700 μιη with a peak sensitivity in the range of 1.5 μιη. 4, in turn, the course 9 of the current density of the infrared sensor according to Example 2 is compared with the current density curve 10 of a comparison sensor without a structured surface layer of silicon, wherein the irradiation conditions were selected according to Example 1.

Example 3 A silicon substrate according to Examples 1 and 2 is subjected to electrochemical anodization in an electrolyte consisting of 0.25M tetrabutylammonium perchlorate in 2M HF acetonitrile to form a porous surface layer. After drying and cleaning according to known methods, the silicon substrate is heated to 580 ° C. in vacuo by flash-lamp annealing and then cooled to 70 ° C. before the substrate has reacted in the same way. In previous examples, an organic semiconductor layer of 6,6'-dibromindigo is coated to a thickness between 20 and 40 nm. The manufactured infrared sensor has a responsiveness beginning at 2700 μιη. Example 4

A p-doped, <100> -oriented silicon with a charge carrier density in the range from 10 ¹⁷ to 10 ²⁰ cm ^-3 is coated with an organic semiconductor layer according to Example 1. However, the structuring of the surface layer of the silicon substrate takes place by an anisotropic etching method according to Example 2. In FIG. 3, the current density profile 1 1 of an infrared sensor fabricated on the basis of this example is shown by dash-dotted lines.

Example 5

The p-doped, monocrystalline, <100> -oriented silicon substrate with a charge carrier density in the range between 10 ¹⁷ to 10 ²⁰ cm ^-3 is provided with a structured surface layer according to Example 1. However, as an organic semiconductor layer, an N, N ' Dimethyl-3,4,9,10-perylenetetracarboxylic diimide used.

Example 6

A polycrystalline silicon is deposited on a substrate, preferably quartz glass or a glass of high optical quality, by a chemical vapor deposition method or by a method other than silicon. The desired p-type doping is initiated and an ohmic metal contact is applied. The porous surface layer of the silicon layer is provided by means of electrochemical or chemical processes in a region which determines the active range of the infrared sensor. According to a standardized cleaning method, an organic semiconductor layer of 6,6'-dibromoindigo is applied before the semiconductor layer is provided with a metal contact.

Example 7 A polycrystalline silicon is used as the active layer of a substrate according to Example 6. After the porous surface layer is formed, an existing pore-expanding method is used to enlarge the pores so that the incident light can be better utilized at the desired near-wavelength wavelength.

Example 8 A p-doped, <100> oriented silicon with a carrier density in the range of 10 ¹⁷ to 10 ²⁰ cm ^-3 is provided with an electrode of vapor-deposited aluminum, a metal-supported etch using metallic nanoparticles, preferably silver , which are physically or chemically deposited on the silicon surface to be subsequently exposed to a solution of hydrogen peroxide and fluorine ions, this method results in nanowire-like column surface morphology After this nanostructuring of the surface layer, the substrate becomes again after drying and cleaning a vacuum heating by flash lapping to 580 ° C and subsequent cooling to 70 ° C exposed before an organic semiconductor layer of N, N'-dimethyl-3,4,9,10 perylenetetracarboxylic diimide is applied in a thickness between 20 and 200 nm An infrared sensor manufactured in this way r has a high sensitivity in the range of 1, 5 μιη.

From FIG. 3, the dashed line current density curve 12 of an infrared sensor fabricated on the basis of this example can be taken.

Example 9

It is provided as in Example 8, a nanowire structure of the silicon substrate. However, a monocrystalline, <1 1 1> -oriented silicon is used.

Claims

claims

1 . Optoelectronic infrared sensor with two connected to one electrode (3, 4), a heterojunction forming semiconductor layers, namely a p-doped silicon layer (1) and an organic semiconductor layer (2) on the silicon layer (1), characterized in that the organic semiconductor layer (2) on a nanostructured and / or microstructured surface layer (6) of the silicon layer (1) is provided and this covers the entire surface.

2. Optoelectronic infrared sensor according to claim 1, characterized in that a semiconductor with hydrogen bridge bonds is used as organic semiconductor layer (2).

3. Optoelectronic infrared sensor according to claim 1 or 2, characterized in that as silicon layer (1) a p-doped silicon having a <100> - or <1 1 1> orientation is provided.