Repeatable Room Temperature Negative Differential Resistance in AlN/GaN Resonant Tunneling Diodes Grown on Sapphire

Abstract

material systems such as wide tunable direct bandgap, inherent fast carrier dynamics, fast carrier transport, high breakdown fields, robust antiirradiation, and strong chemical stability, RTDs based on III-nitride are expected to provide better tunability of resonant tunneling compared with conventional material platforms such as AlGaInAs and AlGaInSb. [1][2][3][4][5][6] Besides, III-nitride materials are characterized by their large longitudinal optical (LO) phonon energies, making them promising candidates for room temperature terahertz quantum cascade lasers (THz-QCLs). [7] As the simplest quantum device adopting resonant tunneling, RTDs form the fundamental background to understand the quantum confinement and vertical transport processes in nitride-based supperlattices, an essential forestep for the realization of III-nitride-based THz-QCLs and quantum cascade detectors. [8][9][10] However, the demonstration of resonant tunneling in III-nitrides remained a challenge until recently. Due to high dislocation densities in heteroepitaxial GaN templates/buffer layers, current-voltage (I-V) behaviors in earlier reports exhibited noteworthy impact from trap states depending on scan directions and times, where the occurrences of negative differential resistance (NDR) were accidental, irreproducible and could not be easily correlated with resonant tunneling. [11][12][13][14][15][16][17][18][19] Demonstrations of clear and repeatable NDR from resonant tunneling in III-nitride based RTDs have been limited to those grown on high quality freestanding (FS) GaN substrates, i.e., through homoepitaxy, with either lowaluminum content AlGaN barriers measured at cryogenic temperature, or AlN barriers measured at room temperature. [20][21][22][23][24] Several motivations exist to grow RTD on sapphire substrates. First, sapphire substrates are more cost-friendly and easier to realize large-size wafer as well as mass production, and could directly lead to a monolithic integration of RTDs with the increasingly sophisticated high frequency devices fabricated on sapphire and even silicon substrates. Second, unlike FS GaN substrates which are usually n-type without intentionally doping, sapphire substrates are inherently insulating, very Resonant tunneling diodes (RTDs) are candidates for high power terahertz oscillators, and form the basis for understanding the quantum confinement and vertical transport in quantum structures such as quantum cascade lasers and quantum cascade detectors. In this work, repeatable negative differential resistance (NDR) is achieved in AlN/GaN RTDs grown on sapphire substrate by plasma-assisted molecular-beam epitaxy. Two reproducible NDR regions sequentially following two preresonance replicas are demonstrated at room temperature. A current region exhibiting negative correlation with temperature and oscillation-like features is first identified under reverse bias, which is interpreted as a combined contribution of weak resonant tunneling channels through different bound states in the well. The revealed peak...

Growth and Characterization of GaN/AlN Resonant Tunneling Diodes for High‐Performance Nonvolatile Memory

“…However, GaN/AlN or GaN/AlGaN heterointerfaces having fine flatness in an atomic level, which can be realized by molecular beam epitaxy techniques, are essential to obtain NDRs with high peak‐to‐valley ratios for terahertz oscillators, as reported by the previous studies. [ 19–23 ] Therefore, we are investigating a new nonvolatile memory using the intersubband transitions and electron accumulation in GaN/AlN RTDs and its growth method based on metalorganic vapor‐phase‐epitaxy (MOVPE) techniques.…”

Controlling Phase‐Coherent Electron Transport in III‐Nitrides: Toward Room Temperature Negative Differential Resistance in AlGaN/GaN Double Barrier Structures

“…Under forward bias, two pre‐resonance replicas are also identified before each resonant peak, similar to what we have observed in AlN barrier RTDs, and could be ascribed to resonant tunneling between quasi‐scattering states in the accumulation layer with different bound states in the well. [ 25 ] Furthermore, at room temperature, resonant tunneling with a well‐pronounced current resonance and a negative differential conductance region is observed, with a PVCR of ≈1.2 and peak current density of ≈10 kA cm −2 . Similar room temperature NDRs have been reproduced in other devices from S3 with PVCR values in the range of 1.1–1.3.…”

“…It is worth mentioning that the low temperature PVCR value in such DA barrier RTDs is equal to or even higher than the reported values in AlN barrier RTDs and is one of the highest among those reports showing reproducible NDR. [ 13–26 ]…”

“…[ 14 ] Previously, we have also reported stable NDR in AlN barrier RTDs at room temperature but still only at cryogenic temperature for AlGaN barrier RTDs. [ 25,26 ]…”

Three Subband Occupation of the Two‐Dimensional Electron Gas in Ultrathin Barrier AlN/GaN Heterostructures

“…[ 8–10 ] The large AlN barrier introduces a high‐density 2DEG at the heterointerface, which forms quantized subbands in the quantum well and stimulates extensive studies for resonant tunneling diodes (RTDs) and other optical devices. [ 11–14 ] It is known that multi‐subbands can induce intersubband scattering, which will cause a lowering of carrier mobility, while high mobility is a decisive parameter to HEMTs. Meanwhile, the occupation and position of the subbands will influence the performance of RTDs and other optical devices, for the tunneling effect and intersubband transition that play key roles in their transport properties.…”