First polarization-engineered compressively strained AlInGaN barrier enhancement-mode MISHFET

Abstract

One current focus of research is the realization of GaN-based enhancement-mode devices. A novel approach for the realization of enhancement-mode behaviour is the utilization of polarization matching between the barrier and the GaN buffer. Yet, the utilization of a quaternary barrier combining polarization engineering together with a large conduction band offset has not been demonstrated so far. Here, epitaxially grown, compressively strained AlInGaN is applied as a nearly polarization-matched barrier layer on GaN resulting in enhancement-mode operation. The insulated-gate devices are fabricated gate-first with Al 2 O 3 as gate dielectric. Passivated metal insulator semiconductor heterostructure field effect transistors yielded threshold voltages (V th ) of up to +1 V. The devices withstand negative and positive gate-biased stress and a positive V th is maintained even after long-time negative bias stress.

Polarization-Engineered Enhancement-Mode High-Electron-Mobility Transistors Using Quaternary AlInGaN Barrier Layers

“…Details on the processing and the different device concepts are published elsewhere. 8,19 The different device geometries make direct comparison quite difficult. The varying distance of the gate contact from the 2DEG is the most relevant difference in the device design.…”

“…Further details on the electrical performance of these devices can be found elsewhere. 8,21 The theoretically smaller conduction-band offset for sample B, due to the lower bandgap of 3.56 eV in comparison with 3.81 eV for sample A, might negatively impact electron confinement in the 2DEG, which could lead to higher leakage currents. On the other hand, nanoscale phase separation is stronger in quaternary layers with higher In contents.…”

“…7,12 The AlInGaN/ GaN heterostructures of sample series 1 were capped with a thin (12 nm to 36 nm) GaN film for process-relevant issues, as reviewed elsewhere. 8 Rutherford backscattering spectrometry (RBS) using 1.4-MeV He + ions at scattering angle of 170°w as performed to acquire reliable information about the AlInGaN thickness and the exact depthresolved composition. Details of the experimental setup were reported elsewhere.…”

“…6,7 Compressively strained AlInN and AlInGaN layers have been used to generate a piezoelectric polarization which compensates a high spontaneous polarization to lower the 2DEG density and realize e-mode operation. 8,9 However, device performance is limited by the inferior crystal quality caused by the high In content. Further, barrier layers under high compressive strain show effects such as relaxation and In pulling, which degrade device characteristics even further and impede process control and reproducibility.…”

Electroreflectance characterization of AlInGaN/GaN high-electron mobility heterostructures

“…For example, the use of quaternary Al x ln y GcLi_ x _yN alloys should allow almost independent control of the lattice parameter and energy band gap by varying the indium and aluminium compositions [1,2]. This advantage can lead to improvements of the performance of electronic devices as well as to completely new design possibilities beyond what is possible with ternary layers, especially for UV light emitting diodes [3], and radio-frequency high-power transistors [4][5][6][7].…”