Erica A. Douglas

An AlN/Al0.85Ga0.15N high electron mobility transistor

An AlN barrier high electron mobility transistor (HEMT) based on the AlN/Al0.85Ga0.15N heterostructure was grown, fabricated, and electrically characterized, thereby extending the range of Al composition and bandgap for AlGaN channel HEMTs. An etch and regrowth procedure was implemented for source and drain contact formation. A breakdown voltage of 810 V was achieved without a gate insulator or field plate. Excellent gate leakage characteristics enabled a high Ion/Ioff current ratio greater than 107 and an excellent subthreshold slope of 75 mV/decade. A large Schottky barrier height of 1.74 eV contributed to these results. The room temperature voltage-dependent 3-terminal off-state drain current was adequately modeled with Frenkel-Poole emission.

Inductively coupled BCl3/Cl2/Ar plasma etching of Al-rich AlGaN

Varying atomic ratios in compound semiconductors is well known to have large effects on the etching properties of the material. The use of thin device barrier layers, down to 25 nm, adds to the fabrication complexity by requiring precise control over etch rates and surface morphology. The effects of bias power and gas ratio of BCl3 to Cl2 for inductively coupled plasma etching of high Al content AlGaN were contrasted with AlN in this study for etch rate, selectivity, and surface morphology. Etch rates were greatly affected by both bias power and gas chemistry. The authors detail the effects of small variations in Al composition for AlGaN and show substantial changes in the etch rate with regard to bias power as compared to AlN.

Reactive sputter deposition of piezoelectric Sc0.12Al0.88N for contour mode resonators

Substitution of Al by Sc has been predicted and demonstrated to improve the piezoelectric response in AlN for commercial market applications in radio frequency filter technologies. Although cosputtering with multiple targets have achieved Sc incorporation in excess of 40%, industrial processes requiring stable single target sputtering are currently limited. A major concern with sputter deposition of ScAl is the control over the presence of non-c-axis oriented crystal growth, referred to as inclusions here, while simultaneously controlling film stress for suspended microelectromechanical systems (MEMS) structures. This work describes 12.5% ScAl single target reactive sputter deposition process and establishes a direct relationship between the inclusion occurrences and compressive film stress allowing for the suppression of the c-axis instability on silicon (100) and Ti/TiN/AlCu seeding layers. An initial high film stress, for suppressing inclusions, is then balanced with a lower film stress deposition to control total film stress to prevent Euler buckling of suspended MEMS devices. Contour mode resonators fabricated using these films demonstrate effective coupling coefficients up to 2.7% with figures of merit of 42. This work provides a method to establish inclusion free films in ScAlN piezoelectric films for good quality factor devices.Substitution of Al by Sc has been predicted and demonstrated to improve the piezoelectric response in AlN for commercial market applications in radio frequency filter technologies. Although cosputtering with multiple targets have achieved Sc incorporation in excess of 40%, industrial processes requiring stable single target sputtering are currently limited. A major concern with sputter deposition of ScAl is the control over the presence of non-c-axis oriented crystal growth, referred to as inclusions here, while simultaneously controlling film stress for suspended microelectromechanical systems (MEMS) structures. This work describes 12.5% ScAl single target reactive sputter deposition process and establishes a direct relationship between the inclusion occurrences and compressive film stress allowing for the suppression of the c-axis instability on silicon (100) and Ti/TiN/AlCu seeding layers. An initial high film stress, for suppressing inclusions, is then balanced with a lower film stress deposition to c...

Al 0.45 Ga 0.55 N/Al 0.30 Ga 0.70 N high electron mobility transistors with Schottky gates and small subthreshold slope factor

Emerging ultrawide bandgap semiconductor materials are logical candidates for applications that exploit the large critical electric field (E<inf>C</inf>) associated with these devices. For semiconductor devices, E<inf>C</inf> scales approximately as E<inf>g</inf>^{2 5} [1]. With a 25% larger bandgap and an approximately 73% larger E<inf>C</inf> than GaN, Al<inf>0.3</inf>Ga<inf>0.7</inf>N-channel high election mobility transistors (HEMTs) might be viable candidates for harsh environment electronics or short wavelength photo-transistors. In either case, transistor quality factors such as minimal off-state leakage currents and subthreshold slope factor are important metrics.

Volumetric Imaging and Characterization of Focusing Waveguide Grating Couplers

Volumetric imaging of focusing waveguide grating coupler emission with high spatial resolution in the visible (

An AlN/Al 0.85 Ga 0.15 N high electron mobility transistor with a regrown ohmic contact

{{\lambda \,= \,637.3\,\text{nm}}}

Effect of precursors on propagation loss for plasma-enhanced chemical vapor deposition of SiN x :H waveguides

) is demonstrated using a scanning near-field optical microscope with long z-axis travel range. Stacks of 2-D images recorded at fixed distance from the device are compiled to yield 3-D visualization of the light emission pattern and enable extraction of parameters, such as spot size, angle of emission, and focal height. Measurements of such parameters are not prevalent in the literature yet are necessary for efficacious design and integration. It is observed that finite-difference time-domain simulations based on fabrication layout files do not perfectly predict in-hand device behavior, underscoring the merit of experimental validation, particularly for critical application.

Chemical downstream etching of Ge, Si, and SiNx films

The performance and efficiency of power devices depends on both high breakdown voltage and low on-state resistance. For semiconductor devices, the critical electric field (EC) affecting breakdown scales approximately as Eg25 [1], making the wide bandgap semiconductor materials logical candidates for high voltage power electronics devices. In particular, AlGaN alloys approaching AlN with its 6.2 eV bandgap have an estimated EC approaching 5x that of GaN. This factor makes AlN/AlGaN high election mobility transistors (HEMTs) extremely interesting as candidate power electronic devices. Until now, such devices have been hampered, ostensibly due to the difficulty of making Ohmic contacts to AlGaN alloys with high Al composition. With the use of an AlN barrier etch and regrowth procedure for Ohmic contact formation, we are now able to report on an AlN/AlGaN HEMT with 85% Al.

Review—Ultra-Wide-Bandgap AlGaN Power Electronic Devices

This work investigates the role of precursor gas chemistry, SiH4/NH3/N2, on hydrogen incorporation into PECVD H:SiNx for optical applications. The largest reduction in of N-H bond density is shown to respond from SiH4 flow, indicating that all precursor gases must be optimized for low loss waveguides. A linear correlation of N-H bond density with propagation losses in SiNx waveguides is observed, allowing for a propagation loss to be estimated by N-H bond density without waveguide fabrication. With proper optimization of process parameters, we are able to obtain propagation losses as low as −1.6 dB/cm at 1550 nm without a thermal anneal.

High Temperature Operation of Al0.45Ga0.55N/Al0.30Ga0.70N High Electron Mobility Transistors

This work reports on selective isotropic dry etching of chemically vapor deposited Ge thin film, release layers using a Shibaura chemical downstream etcher with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si, and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates was measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching. Observation of preferential etching of Ge in the presence of Si and SiNx is also observed with lateral etch rates reaching 19.2 μm/min for the Ge layers. Results presented here demonstrate the use of Ge as a microelectromechanical systems device dry release layer in the presence of Si and SiNx making it a highly advantageous technology, especially for optical devices.