Terahertz antenna and method for producing a terahertz antenna

Abstract

A terahertz antenna includes at least one photoconductive layer which generates charge carriers upon irradiation of light and two electroconductive antenna elements via which an electric field can be applied to at least one section of the photoconductive layer. The photoconductive layer being doped with a dopant in a concentration of at least 11018 cm3, the dopant being a transition metal. The photoconductive layer is produced by molecular beam epitaxy at a growth temperature of at least 200 C. and not more than 500 C., the dopant being arranged in the photoconductive layer such that it produces a plurality of point defects.

Claims

1. A terahertz antenna, comprising: at least one photoconductive layer which generates charge carriers upon irradiation of light; and two electroconductive antenna elements via which an electric field can be applied to at least one section of the photoconductive layer, wherein: the photoconductive layer being doped with a dopant in a concentration of at least 110.sup.18 cm.sup.3, the dopant being a transition metal, and the photoconductive layer is produced by molecular beam epitaxy at a growth temperature of at least 200 C. and not more than 500 C., the dopant being arranged in the photoconductive layer such that it produces a plurality of point defects.

2. The terahertz antenna according to claim 1, wherein the plurality of dopant atoms each are arranged in the photoconductive layer in the form of a point defect or substantially all dopant atoms each are arranged in the photoconductive layer in the form of a point defect.

3. The terahertz antenna according to claim 1, wherein the photoconductive layer has no or only a small number of dopant clusters.

4. The terahertz antenna according to claim 1, wherein the concentration of the dopant is at least 510.sup.18 cm.sup.3, at least 110.sup.19 cm.sup.3 or at least 110.sup.20 cm.sup.3.

5. The terahertz antenna according to claim 1, wherein the photoconductive layer is configured such that it generates charge carriers upon irradiation of light in a wavelength range between 1000 and 1650 nm.

6. The terahertz antenna according to claim 1, wherein the photoconductive layer is formed of (In, Ga)As, (In, Ga)(As, P) or (In, Ga, Al)(As, P).

7. The terahertz antenna according to claim 1, wherein the photoconductive layer has a thickness of at least 100 nm, at least 300 nm or at least 500 nm.

8. The terahertz antenna according to claim 1, wherein the photoconductive layer is grown on a semi-insulating substrate.

9. The terahertz antenna according to claim 1, wherein the dopant is iron, ruthenium, rhodium and/or iridium.

10. The terahertz antenna according to claim 1, wherein the photoconductive layer forms a mesa structure, wherein the antenna elements each are connected to a side wall of the mesa structure.

11. A terahertz converter for generating and/or receiving terahertz radiation, wherein the terahertz converter includes at least one terahertz antenna according to claim 1.

12. The terahertz converter according to claim 11, comprising a first and a second terahertz antenna, which each are configured according to any of the preceding claims, wherein the photoconductive layers of the first and the second terahertz antenna are sections of a common photoconductive layer.

13. A method for producing a terahertz antenna, comprising the following steps: producing at least one photoconductive layer which generates charge carriers upon irradiation of light; doping of the photoconductive layer with a dopant in a concentration of at least 110.sup.18 cm.sup.3, the dopant being a transition metal; and producing two electroconductive antenna elements, via which an electric voltage can be applied to at least one section of the photoconductive layer, wherein: the photoconductive layer is produced by molecular beam epitaxy at a growth temperature of at least 200 C. and not more than 500 C., and doping is effected during the process of epitaxy.

14. The method according to claim 13, wherein the growth temperature lies between 250 C. or 300 C. and 500 C.

15. The method according to claim 13, wherein the growth temperature is not more than 450 C. or not more than 400 C.

16. The method according to claim 13, wherein after growing the photoconductive layer a tempering step is performed.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in detail below by means of exemplary embodiments with reference to the Figures.

(2) FIG. 1 schematically shows a band diagram of a photoconductive InGaAs layer grown on an indium phosphide substrate.

(3) FIG. 2 shows a top view of a terahertz antenna according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

(4) The band diagram shown in FIG. 1 refers to a possible configuration of the photoconductive layer of the terahertz antenna according to the invention. The photoconductive layer here is configured in the form of an InGaAs layer which has been grown on an InP substrate in a lattice-matched manner. Between the InGaAs layer and the InP substrate an InAlAs buffer layer is present. In the diagram, the respective band gaps are indicated (CB: conduction band; VB: valence band).

(5) In the middle of the band gap of the InGaAs layer there is the energy level (broken line) of point-like recombination centers, which were produced by doping the InGaAs layer with a transition metal (e.g. Fe).

(6) When light (hv), e.g. in the form of a laser pulse with a center wavelength of 1550 nm, impinges on the InGaAs layer, electrons from the valence band VB are excited into the conduction band CB and correspondingly electron-hole pairs are produced.

(7) The excited electrons are accelerated by a voltage applied to the InGaAs layer, wherein the accelerated electrons emit terahertz radiation. The produced electron-hole pairs recombine in the recombination centers, wherein the recombination time is very short due to the point-like recombination centers produced by doping. The InAlAs buffer layer and the substrate are not involved in the generation of the electron-hole pairs due to their larger band gap.

(8) FIG. 2 shows a top view of a terahertz antenna 1 according to the invention. The terahertz antenna 1 includes a photoconductive semiconductor layer 11 produced by MBE on a substrate 12 (e.g. a semi-insulating InP substrate), which forms a cuboid mesa structure. In addition, the photoconductive semiconductor layer 11 has a higher concentration (at least 110.sup.18 cm.sup.3) of a dopant (e.g. iron). It is conceivable that the photoconductive semiconductor layer 11 is formed of doped InGaAs or includes such a material.

(9) In addition, the terahertz antenna 1 has a first and a second strip-like antenna element 21, 22 which each is arranged on the substrate 12. The antenna elements 21, 22 are formed of a metal and were deposited (e.g. vapor-deposited) on the substrate 12.

(10) Furthermore, the antenna elements 21, 22 extending parallel to each other each are electrically connected to one side of the photoconductive semiconductor layer 11, so that via the antenna elements 21, 22 a voltage can be applied to the semiconductor layer 11. For the connection of a voltage source the antenna elements 21, 22 each have contact surfaces 210, 220.