III-V Resonant Tunneling Diode (RTD) Structure *S
III-V compounds are the earliest material systems used for resonant tunneling diode (RTD) structures and the most extensively studied material systems. Compared to other RTD material systems, they have the best electrical parameters (current peak to valley ratio, peak current density, negative resistance characteristics, etc.) and are the most promising RTD material systems. PAM-XIAMEN can produce GaAs or InP based epitaxial wafers with resonant tunneling diode structure, more parameters please refer to the following tables:
1. Resonant Tunneling Diode Structure on III-V Material System
1) GaAs based RTD Structure
| Epi Layer | Thickness | Doping Concentration |
| n-GaAs | – | – |
| GaAs | 5nm | – |
| In0.1Ga0.9As | – | – |
| GaAs | – | – |
| AlAs | – | – |
| GaAs | – | – |
| In0.1Ga0.9As | – | – |
| GaAs | – | – |
| AlAs | – | – |
| GaAs | – | UD |
| In0.1Ga0.9As | – | – |
| GaAs | – | – |
| n-GaAs | – | – |
| n+GaAs | – | – |
| SI-GaAs |
2) InP based RTD Structure
| Epi Layer | Thickness | Doping Concentration |
| n+-InGaAs | – | – |
| n+-InGaAs | – | – |
| un-InGaAs | – | – |
| AlAs | – | – |
| InGaAs | – | – |
| AlAs | – | – |
| un-InGaAs | – | – |
| n+-InGaAs | – | 1×1018cm-3 |
| n+-InGaAs | – | – |
| Semi-insulating InP Substrate |
2. III-V Compound Material System for RTD
The widely used III-V group compound RTD material systems today mainly include:
2.1 GaAs based AlxGa1-xAs/InyGa1-yAs Resonant Tunneling Diode
The AlxGa1-xAs/GaAs heterojunction, which adopts a double barrier single well (DBSW) structure, is the earliest material used by researchers to manufacture RTDs. This is also the most thorough numerical analysis and research on theoretical models and transport processes, the most mature epitaxial growth technology, and the most widely used resonant diode material system in device and circuit applications.
Theoretical research and experiments on resonant tunneling have shown that the band shift (bandgap difference) of a double barrier single well structure is the key to determining the peak to valley current ratio and negative resistance of RTDs. In the AlxGa1 xAs/GaAs heterojunction, the bandgap width of the AlxGa1 xAs barrier changes with the change of x value, resulting in a change in the conduction band offset (conduction band discontinuity) between the barrier and well. The larger the Al component in the barrier, the greater the conduction band offset between the barrier and well, and the greater the peak to valley current ratio (PVCR) of the device, which can shorten the switching time of the quantum tunneling diode and improve the operating frequency. In addition, doping In atoms into GaAs potential wells can deepen the wells, increase the conduction band shift between barrier wells, effectively suppress scattering current, and reduce the potential well width and increase tunneling current density without changing the peak voltage. Therefore, growing InGaAs quantum wells in GaAs quantum wells can effectively improve the peak to valley current ratio. By combining the advantages of the two materials, high-performance AlAs/InGaAs/AlAs RTDs can be produced.
2.2 InP based Resonant Tunneling Diode
Compared with the GaAs based AlAs/In 0.1 GaAs heterojunction, the InP based AlAs/In 0.53 GaAs heterojunction has a larger band shift (conduction band discontinuity), making it possible to prepare RTD devices with higher PVCR and higher peak current density (PCD). The above structure is a commonly used InP based AlAs/In GaAs RTD material structure. Usually, the room temperature PVCR of GaAs/AlGaAs/InGaAs quantum resonant tunneling diode is 7, while the room temperature PVCR of InP/AlInAs/InGaAs RTDs can reach up to 20, which can further improve the operating frequency of RTDs. Recently, Suzuki et al. reported that an oscillator with a resonance frequency of 900GHz was fabricated using InP/AlGaAs/InGaAs RTDs.
In recent years, more and more high-speed and high-frequency devices such as HEMT, HBT, optoelectronic switches, and detectors have chosen to be fabricated on InP substrates due to the ability to grow larger In component InGaAs materials with higher mobility. By combining the high-performance, multifunctional, and high integration characteristics of RTD, InP RTD and the aforementioned InP based devices can be integrated into high-frequency, high-speed analog circuits and digital circuits with higher functionality and integration through single chip or mixed integration, such as RTD/HBT integrated MMIC, RTD/HBT integrated MOBILE digital circuits (trigger circuits, frequency dividers), RTD/HEMT integrated multi value inverse logic circuits, and RTD/CMOS integrated logic circuits.
2.3 InAs/AlSb/GaSb Resonant Interband Tunneling Diode
The resonant interband tunneling diode (RITD) made of InAs/AlSb/GaSb material system has also attracted some attention due to its small peak voltage (0.5v) and peak current density (mA level), with a switching time of only 1ps. S ö derstr ö m et al. reported that at room temperature, the peak to valley ratio in this double barrier structure was 3.2:1, the peak current density was 3.7×105 A/m2, and the resonance frequency could reach 712GHz, which was the highest frequency among all solid-state oscillators at that time. Due to the band structure of InAs/AlSb/GaSb, this type of RITD greatly suppresses valley current compared to traditional RTDs, resulting in higher peak to valley ratios, reaching 20:1 at room temperature and 150:1 at low temperature.
3. Regarding Resonant Tunneling Diodes Principle
Resonant tunneling diode is a type of diode with a resonant tunneling structure, in which electrons can tunnel through certain resonant states at specific energy levels. The current voltage characteristics typically exhibit a negative differential resistance region. Its characteristic lies in the highly nonlinear current voltage (IV) characteristics, typically including a negative differential resistance (NDR) region and two positive differential resistance regions, as shown in Fig. 1.
This nonlinearity is the result of quantum mechanical resonance tunneling of electrons/holes through devices, although electron manipulation is usually preferred due to high correlated drift mobility, resulting in higher current density and maximum operating frequency. The precise shape of IV characteristics depends on different factors such as device size, material composition, epitaxial structure, and temperature. The characteristics of the negative differential resistance region are Ip and Iv, which are the peak current and valley current, as well as the corresponding voltages Vp and Vv, respectively. In addition, it can be described using ∆ I=Ip − Iv (peak to valley current difference), ∆ V=Vp − Vv (peak to valley voltage difference), and PVCR=Ip/Iv (peak to valley current ratio). The electrical span of the NDR region determines the theoretical maximum RF power that the RTD device can transmit to the load. The actual RF output power depends on different factors, such as operating frequency, device and circuit parasitic components, and impedance matching factors.
Fig. 1 Schematic diagram of RT-IV characteristics of general RTD devices: assuming the first and second quasi bound resonant energy levels in a quantum well
The fundamental frequency of the tunneling resonant diode is close to 2 THz. Its main limitation is low output power, usually in the microwatt range, but the terahertz power generated by this technology is now in the milliwatt (mW) range, making practical application of resonant tunneling diode in fields such as imaging and gigabit wireless communication systems.
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