DE102016215331B4 - Optoelectronic mixer element - Google Patents

Abstract

Optoelectronic mixer element, consisting of a p-doped base substrate (1) with a high band gap, two separate n + doped areas (2a, 2b) being built up within the base substrate (1), followed by a p-doped stop layer (3) on top of the base substrate (1) ), an intrinsic absorber layer (4) and a p + doped filter layer (5), with the stop layer (3) and absorber layer (4) made of a material with a band gap <0.8 eV and the filter layer (5) made of a material with a band gap> 1.2 eV are built up.

Description

The invention relates to an optoelectronic mixer element and a method for operating such according to the preamble of the independent claims.

From the DE 197 04 496 A1 a mixer element is already known which demodulates received radiation on the basis of modulation and accumulation gates. Such a so-called photonic mixer is used, for example, in time-of-flight camera systems that obtain a time of flight from the phase shift of an emitted and received radiation.

Furthermore, from US 2005/0 199 976 A1 a photodiode array which can be illuminated from the rear is known for the area of optical communication for receiving a large number of optical signals, in which separate n + doped areas are built up within a p-doped base substrate and these are connected to an n- Adjacent doped absorber layer.

The object of the invention is to increase the efficiency of the demodulation.

The object is achieved in an advantageous manner by the optoelectronic mixer element and method according to the invention according to the preamble of the independent claims.

An optoelectronic mixer element is advantageously provided, consisting of a p-doped base substrate with a high band gap, with two separate n + doped regions being built up within the base substrate,
building on the base substrate, there is a p-doped stop layer, an intrinsic absorber layer and a p + -doped filter layer,
wherein the stop layer and absorber layer are composed of a material with a low band gap and the filter layer is composed of a material with a high band gap.

This arrangement has the advantage that the structure can be controlled through the choice of the band gaps so that the filter layer absorbs visible radiation, for example, and is transparent to IR radiation, which can then be effectively converted into charge carriers in the absorber layer.

The optoelectronic mixer element is particularly advantageously constructed from III-V compound semiconductors.

This procedure is advantageous because due to the high absorption coefficients of the III-V compound semiconductors, the incident radiation can be converted particularly efficiently into charge carriers. Furthermore, these materials have a particularly high electron mobility, so that such an element can be operated with very high modulation frequencies up into the GHz range.

The base substrate and the filter layer are preferably composed of indium phosphide InP and the stop layer and absorber layer are composed of indium gallium arsenide In _x-1 Ga _x As.

It is particularly useful to form a stop layer between the base substrate and the absorber layer to prevent a space charge zone between diodes A and B from penetrating through. This stop layer prevents the expansion of the space charge zone of the diode connected to Vlow.

It is also advantageous to design the filter layer to absorb short-wave light, preferably light with a wavelength of less than 900 nm.

This procedure has the advantage that essentially only the desired useful light contributes to the generation of charge carriers in the subsequent layers.

A pixel is particularly advantageously equipped with the aforementioned optoelectronic mixer element, the pixel having storage elements that can be read out for accumulating the charges detected by diodes A and B.

A method for operating an optoelectronic mixer element or pixel according to the aforementioned type, in which a reference potential V_low is applied to the base layer and the filter layer, is also advantageous,
wherein, in order to demodulate a light incident on the optical mixer element, the cathodes of diodes A and B are placed in opposite directions and alternately to a positive potential V_high and to reference potential V_low.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings.

In the following description of the preferred embodiments, the same reference symbols designate the same or comparable components.

1 shows schematically a structure of an optoelectronic mixer element according to the invention. In terms of the basic structure, this mixer element has two pin diodes A, B on a base substrate 1 realized. The cathodes of the two diodes A, B are as separate n + doped areas 2a , 2 B in the base substrate 1 built up while the intrinsic layer and the p + doped anode are shared. To shield unwanted space charges is between the base substrate 1 and thus also the n + areas 2a and 2 B a p-doped stop layer 3 arranged.

As a base substrate 1 a material with a high band gap, for example indium phosphide InP, is provided which has p-doping. Inside the base substrate 1 Two separate, highly doped n + areas are implemented on a top side, each of which forms a cathode of a pin diode A, B. The p-doped base layer 1 and the n + areas 2a , 2 B each have a metallization for electrical contacting.

Building on the top of the base substrate 1 a p-doped stop layer follows 3 , an intrinsic absorber layer 4th and a p + doped filter layer 5 , which also serves as a common anode for the two pin diodes A, B. The filter layer 5 also has a metallization for electrical contacting.

Stop shift 3 and the intrinsic absorber layer 4th are made of the same material with a low band gap preferably <0.8 eV, eg In _x-1 Ga _x As.

The filter layer 5 is composed of a material with a high band gap, preferably> 1.2 eV, eg InP. By suitable selection of the materials and the band gap, the filter layer can be designed in particular for the absorption of short-wave radiation <900 nm. As already described, the filter layer is used 5 as the common anode of the layers 5 , 4th , 3 and 2a , 2 B built-up pin diodes A, B. When the optoelectronic mixer is operated, this anode is connected to a reference potential V_low. Next to the filter layer 5 , which here serves as the common anode for the pin diode A, B, the p-doped base layer is also located during operation 1 on the reference potential V_low.

In order to prevent reaching through the space charge zone between pin diodes A and B and in particular to the cathode, which is at reference potential V_low, is on the base substrate 1 and thus between the intrinsic absorber layer 4th and the n + areas 2a , 2 B a p-doped stop layer 3 arranged.

The stop layer 3 is designed, doped and dimensioned in such a way that the space charge zone of the cathode switched to V_high penetrates into the absorber layer 4th is as large as possible, but at the same time a penetration of the cathode switched to V_low through the stop layer 3 prevented or as low as possible.

A filter layer is used as the top layer 5 upset. This layer is heavily p-doped. The holes generated there are discharged via the anode. Due to the heavy doping, the generated electrons only have a short lifespan and recombine before they reach the absorber layer 4th reachable.

This configuration has the advantage that in the absorber layer 4th essentially only the charge carriers generated by the useful light contribute to the photocurrent at the pin diodes A, B.

• Die Anoden der Filterschicht 5 und der Basisschicht 1 liegen auf eine Bezugsspannung V_low = 0V. Die beiden Kathoden 2a, 2b der pin-Dioden A, B werden abwechselnd auf ein positives Potenzial V_high und auf die Bezugsspannung V_low = 0V geschaltet. Dabei breitet sich eine Raumladungszone der jeweils auf dem positiven Potenzial Vhigh geschalteten Kathode in die Absorberschicht 4 aus, mit einem Potenzialgefälle innerhalb der Absorberschicht 4 hin zu der auf V_low geschalteten Diode.

The mixer element according to the invention is particularly useful for the construction of a demodulating pixel, in particular for a pixel for determining a phase shift of an emitted and received modulated radiation. For example, the following operating mode would be suitable for demodulation:

• The anodes of the filter layer 5 and the base layer 1 are on a reference voltage V_low = 0V. The two cathodes 2a , 2 B the pin diodes A, B are alternately switched to a positive potential V_high and to the reference voltage V_low = 0V. In the process, a space charge zone of the cathode, which is connected to the positive potential Vhigh, spreads into the absorber layer 4th off, with a potential gradient within the absorber layer 4th towards the diode switched to V_low.

In a preferred, intended use, modulated useful light and unmodulated ambient light fall simultaneously, preferably perpendicularly, onto the filter layer 5 . All spectral components that have a higher photon energy than the band gap of the material of the filter layer are absorbed 5 . The corresponding photogenerated holes are drained through the anode connection. The photo-generated electrons recombine within the filter layer 5 .

All spectral components with a lower energy than the band gap of the filter layer 5 pass the filter layer 5 and get into the absorber layer 4th . Because of the significantly lower band gap according to the invention, electron hole pairs are generated there. The holes become the anode terminals in the base layer 1 and filter layer 5 led away. The electrons arrive along the potential gradient within the absorber layer 4th to the cathode switched to positive potential V_high and can be read out there.

This photocurrent can then be evaluated in a downstream circuit, for example. In particular, for a phase determination, the current flowing through the diodes A, B can be integrated and evaluated according to a time-of-flight principle shown, for example, in DE 197 04 496 A1.

• Vorteilhaft kann eine optische Distanzmessung nach dem Time-of-Flight Prinzip mit Hilfe von Heterojunction-Dioden ausgeführt werden. Bevorzugt ist das Mischerelement aus III-V Verbindungsleitern hergestellt und ermöglichen so hohe Elektronenmobilität und hohe Absorptionseffizienz. Die Aufbringung einer Stoppschicht unterbindet vorteilhaft einen Durchgriff der Raumladungszone von Diode A nach Diode B und begrenzt die Ausdehnung der Raumladungszone der auf V_low geschalteten Diode. Weiterhin erlaubt die aufgebrachte Filterschicht eine Absorption von kurzwelligem Fremdlicht.

In summary, the optoelectronic mixer element according to the invention is characterized by the following aspects:

• An optical distance measurement can advantageously be carried out according to the time-of-flight principle with the aid of heterojunction diodes. The mixer element is preferably made from III-V connecting conductors and thus enable high electron mobility and high absorption efficiency. The application of a stop layer advantageously prevents the space charge zone from reaching through from diode A to diode B and limits the expansion of the space charge zone of the diode connected to V_low. Furthermore, the applied filter layer allows short-wave extraneous light to be absorbed.

List of reference symbols

1

Base substrate, anode

2a

first diode A, cathode

2 B

second diode B, cathode

3

Stop shift

4th

Absorber layer

5

Filter layer, anode

Claims (7)

Optoelectronic mixer element, consisting of a p-doped base substrate (1) with a high band gap, two separate n + doped regions (2a, 2b) being built up within the base substrate (1), building on the base substrate (1) follows a p-doped stop layer (3), an intrinsic absorber layer (4) and a p + doped filter layer (5), wherein the stop layer (3) and absorber layer (4) made of a material with a band gap <0.8 eV and the filter layer (5) are constructed from a material with a band gap> 1.2 eV. Optoelectronic mixer element according to Claim 1 , in which the optoelectronic mixer element is made up of III-V compound semiconductors. Optoelectronic mixer element according to one of the preceding claims, in which the base substrate (1) and the filter layer (5) are made from indium phosphide InP and the stop layer (3) and absorber layer (4) are made from indium gallium arsenide In _1-x Ga _x As. Optoelectronic mixer element according to one of the preceding claims, in which the two separate n + doped regions (2a, 2b) together with the p-doped base substrate (1) form a diode A and diode B, the stop layer (3) between diodes A and B and the absorber layer (4) is arranged. Optoelectronic mixer element according to one of the preceding claims, in which the filter layer (5) is designed to absorb light of less than 900 nm. Pixel with an optoelectronic mixer element according to one of the preceding claims, which has storage elements which can be read out in order to accumulate the charges detected by diodes A and B. Method for operating an optoelectronic mixer element according to Claim 1 to 5 or pixels after Claim 6 , in which a reference potential (V_low) is applied to the base layer (1) and the filter layer (5), with the cathodes of the diodes A and B alternately and in opposite directions to a positive potential (V_high ) and to a reference potential (V_low).

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