Resonant Tunneling Diodes: Mid-Infrared Sensing at Room Temperature

Resonant tunneling diode photodetectors with GaInAsSb absorbers appear to be promising architectures with a simple design for mid-infrared sensing operations at room temperature. We demonstrate how the drift, accumulation and escape efficiencies of photogenerated carriers influence the electrostatic modulation of the sensor’s electrical response.

Over the last few decades, resonant tunnelling diodes (RTDs) have been realized and demonstrated in various materials ranging from semiconductors to oxides [1,2] .The wide range of applications includes highfrequency oscillators in the THz range [3] , logic elements [4] , and high sensitive detectors for strain [5] , temperature [6] and light [7 10] .Especially for light sensing, in uses such as optical molecule and gas spectroscopy or light detection and ranging (LiDAR), there is an increasing demand for highperformance devices operating in the midinfrared (MIR) spectral region.The MIR wavelength range is appealing because several important gases, such as CO2 ( nm), CO ( nm), H2O ( nm), and HCl ( nm) have their absorption lines within this spectral window.
The diode was grown on an ntype Tedoped GaSb (100) substrate by molecular beam epitaxy with a resonant tunnelling structure based on a GaAs0.15Sb0.85/AlSbdoublebarrier structure (DBS) [11] built in proximity to a latticematched Ga0.64In0.36As0.33Sb0.67absorption layer with a cutoff wavelength of nm ( meV onset energy).The band structure is displayed in Figure 1(a).The details of the fabrication process can be found in Ref. [12] .In figure 1(c) the IV curve for dark and under illumination is plotted with the corresponding , which is the voltage difference of the two curves.To explain the photocurrent respectively we consider the electrons accumulated in the prewell, the depletion layers with 3D densities and the photogeneration of electronhole pairs in the absorption layer.Also following the charge drift, the subsequent accumulation of electrons and holes at the right side of the GaInAsSb/GaSb interface and at the DBS and their eventual escape are considered.The current increase for forward bias voltages is related to an electrostatic shift of the voltage drop along the structure produced by the modulation of the charge accumulation [13].This process alters the tunnelling current and leads to the observed .Note that there is a point of maximum response with a nontrivial modulation with voltage.
The nonmonotonic behaviour of respectively the photocurrent is produced by the balance of trapping and escaping efficiencies.The slow decrease of the voltage shift for higher voltages is tuned by the escape rates of the holes through the DBS.The escape rates culminate at the resonant tunnelling of holes represented as a dip in .
Figure 2 (c) and (d) picture the measured photocurrent as a colourgradient map and as a crosssectional view, respectively.The simulated voltage shift (b) fits well to the measured values.The small dip at meV is due to a reduction in the output power of the light source and was consequently not included in the simulated data.In contrast to the dip, the peak at meV emerges from absorption in the GaSb layer.The simulated and measured absorption line of water is well pronounced and confirms that this RTD can be used as a detector for gases in the MIR regime.The absorption for photon energies below the bandgap can be triggered at higher voltages due to the Stark effect, which reduces the effective energy gap with increasing .
In summary, we have characterized he main ingredients that control the selectivity and sensitivity of RTD photosensors, as well as their photoresponse.The role of minority carriers has been correlated to the trapping efficiency and quantum transmission of photogenerated electrons and holes, and the tuning of these effects with external bias and the parameters of the incoming light.The sensor sensitivity can be enhanced by a high trapping efficiency of the minority carriers.Finally, the sensor response to the presence of H2O molecules at room temperature has been unambiguously demonstrated.

Figure 1 (
Figure 1 (a) Band structure and doping profile of the RTD.(b) Currentvoltage characteristics for forward and reverse bias voltage with and without illumination for various optical powers using an incident light of 619 meV (c) Currentvoltage characteristics under dark and illumination conditions, and the extracted value of the voltage shift under illumination.

Figure 1 (
Figure 1 (b) shows the current densities in dark and illumination conditions.One can clearly see the asymmetric photoresponse.In figure 1(c) the IV curve for dark and under illumination is plotted with the corresponding, which is the voltage difference of the two curves.To explain the photocurrent respectively we consider the electrons accumulated in the prewell, the depletion layers with 3D densities and the photogeneration of electronhole pairs in the absorption layer.Also following the charge drift, the subsequent accumulation of electrons and holes at the right side of the GaInAsSb/GaSb interface and at the DBS and their eventual escape are considered.The current increase for forward bias voltages is related to an electrostatic shift of the voltage drop along the structure produced by the modulation of the charge accumulation[13].This process alters the tunnelling current and leads to the observed .Note that there is a point of maximum response with a nontrivial modulation with voltage.The nonmonotonic behaviour of respectively the photocurrent is produced by the balance of trapping and escaping efficiencies.The slow decrease of the voltage shift for higher voltages is tuned by the escape rates of the holes through the DBS.The escape rates culminate at the resonant tunnelling of holes represented as a dip in .