AlN/GaN HEMTs grown by MBE and MOCVD: Impact of Al distribution

Abstract

Binary AlN/GaN high electron mobility transistors (HEMTs) were grown by plasma-assisted molecular beam epitaxy (PA-MBE) as well as metal-organic chemical vapor deposition (MOCVD) and compared with regard to their structural and electrical properties. The investigated structures differ in Al distribution and composition of the AlN barrier due to characteristic differences of the two growth methods such as growth temperature and interface sharpness. While we observe a nearly pure AlN layer and an abrupt interface for MBE growth, a graded "AlN" barrier with a significant amount of Ga is found for the MOCVD grown structures which is reflected by the electrical properties of the HEMT structures. Si-implanted ohmic contacts were formed on MBE as well as MOCVD grown structures. The activation anneal step subsequent to implantation at temperatures ~1100°C changes the observed Al profiles of MBE structures and damages the active region, whereas MOCVD samples react insensitively and thus were able to be further processed. A maximum drain current of ~1.46 mm(-1) at a gate source voltage of +3 V is observed for the processed devices. A current-gain cut-off frequency of 89 GHz and maximum oscillation frequency of 208 GHz were measured, which demonstrate an excellent small-signal performance of AlN/GaN devices with 100nm gate length

Optimization of Metal‐Organic Chemical Vapor Deposition Regrown n‐GaN

“…The Si‐implanted GaN buffer has to be activated by thermal annealing, which is typically done at temperatures where Ga and Al atoms from the channel, barrier, and cap layers tend to diffuse between the layers, which deteriorates the characteristics of the 2DEG formed at the channel/barrier interface, because of increased alloy scattering . Atom diffusion in HEMT structures is clearly seen by secondary ions mass spectrometry (SIMS) and high‐resolution X‐ray diffraction (HRXRD) measurements, when the structures are annealed or after the n‐GaN MOCVD regrowth step, because both are high‐temperature processes.…”

Structural and Optical Properties of GaN Nanowires Formed on Si(111)

“…GaN NWs were grown on Si(111) substrates by a plasma-assisted molecular-beam epitaxy (PA-MBE) with a solid Ga source and a N-plasma cell. A N-plasma flux was obtained by applying an RF generator with a frequency of 13.56 MHz to N gas with a purity of 99.9999 % [20,21]. Before the growth of GaN NWs, native oxide on Si(111) substrates was removed by subsequent thermal annealing at a substrate temperature of 900 o C inside a PA-MBE reactor.…”

High‐Power Microwave GaN/AlGaN HEMTs and MMICs on SiC and Silicon Substrates for Modern Radio Communication

“…The detailed epitaxial structures grown by multi‐wafer MOCVD are described in detail in Ref. . The gate is formed by e‐beam for a T‐gate structure with a length of l g = 100 nm based on the work in Ref.…”