Investigating the bistability characteristics of GaN/AlN resonant tunneling diodes for ultrafast nonvolatile memory

Abstract

The bistability characteristics of GaN/AlN resonant tunneling diodes (RTDs) grown on a sapphire substrate by metalorganic vapor phase epitaxy (MOVPE) were investigated to better understand their physical origin and explore their use in nonvolatile memories. The bistability current-voltage (I-V) characteristics of GaN/AlN RTDs, which were due to intersubband transitions and electron accumulation in the quantum well, were clearly observed over a wide temperature range between 50 and 300 K. However, the I-V characteristics sometimes degraded at temperatures above 250 K. Complex staircase structures were observed in the voltage region showing a negative differential resistance in the I-V curve, and the forward current increased or decreased rapidly as the forward-bias voltage increased. Repeated measurements of the I-V characteristics over the wide temperature range between 50 and 300 K revealed that the bistability characteristics of GaN/AlN RTDs degraded owing to the leakage of electrons accumulating in the quantum well through a deep level in the AlN barrier associated with crystal defects such as dislocations and impurities. Therefore, reduction in crystal defect and impurity densities in the AlN barrier, and a careful design that considers deep levels are important for realizing realize ultrafast nonvolatile memories based on the bistability characteristics of GaN/AlN RTDs.

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

“…This induces the shift of E R1 and E R2 to higher energy and the transition from a high to low transmittivity. [ 14,15 ] Therefore, switching from the ON to OFF state (write memory operation) is realized by applying a forward bias voltage.…”

“…Therefore, we have studied a new nonvolatile memory using the intersubband transitions in GaN/AlN resonant tunneling diodes (RTDs). [ 14–18 ] This new memory, called resonant tunneling random‐access memory (RT‐RAM), has the potential to realize a high‐speed nonvolatile RAM operating at the picosecond time scale and to be used in the high‐speed region in normally off computing systems and the other applications, such as field‐programmable gate array and sensor network systems.…”

“…However, theoretical analysis of band structure and experimental current characteristics for pulse voltages with wide pulse widths have revealed that the bistability was due to the intersubband transitions and electron accumulation in the quantum well instead. [ 15,18 ] Thus, the development of a new nonvolatile memory using the intersubband transitions and electron accumulation in GaN/AlN RTDs has become possible. In addition, this finding might enable us to develop a new material‐based terahertz oscillator using the negative differential resistances (NDRs) in GaN/AlN or GaN/AlGaN RTDs, because the bistability in I – V characteristics can be suppressed by the resonant tunneling through the first resonant level or the second resonant level with a small dipole moment for the first resonant level.…”

New Tunneling Features in Polar III-Nitride Resonant Tunneling Diodes

“…Double-barrier GaN=AlðGaÞN RTDs, being the simplest device to study resonant transport, have been under scrutiny during the past decades with moderate success [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Experiments on AlN-barrier RTDs grown on sapphire templates have shown a region of NDC under forward bias (the bottom contact layer is the reference of the applied voltage).…”

“…Experiments on AlN-barrier RTDs grown on sapphire templates have shown a region of NDC under forward bias (the bottom contact layer is the reference of the applied voltage). However, these devices present nonrepeatable current-voltage (I-V) characteristics [9][10][11][12]. It has been suggested that the high density of defects present in GaN films grown on sapphire (with a typical dislocation density of 10 9 cm −2 ) can act as electron traps, leading to selfcharging effects and preventing coherent transport of carriers.…”