Naotaka Iwata

Laser-induced local activation of Mg-doped GaN with a high lateral resolution for high power vertical devices

A method for laser-induced local p-type activation of an as-grown Mg-doped GaN sample with a high lateral resolution is developed for realizing high power vertical devices for the first time. As-grown Mg-doped GaN is converted to p-type GaN in a confined local area. The transition from an insulating to a p-type area is realized to take place within about 1–2 μm fine resolution. The results show that the technique can be applied in fabricating the devices such as vertical field effect transistors, vertical bipolar transistors and vertical Schottkey diode so on with a current confinement region using a p-type carrier-blocking layer formed by this technique.

Realization of conductive AlN epitaxial layer on Si substrate using spontaneously formed nano-size via-holes for vertical AlGaN high power FET

Summary form only given. If vertical AlGaN FET on Si substrate is realized, high power, high voltage FET beyond SiC and GaN FET is obtained due to the high band gap and high breakdown voltage. For realizing vertical AlGaN FET on Si substrate, conductive AlN buffer layer on Si substrate is indispensable, because AlN buffer layer is necessary for growing AlGaN on Si substrate to avoid large size melt-back of Si substrate by Ga source during the growth. However, AlN is known to be a highly insulating material, and preparation of conductive AlN remained to be a challenge. We have successfully realized conductive AlN buffer layer by forming nano-size spontaneous via-holes. The vertical conductivity through AlN is enhanced about 1000-fold by filling conductive n-AlGaN inside the via-holes. Using the conductive via-holes, we have succeeded in fabricating vertical UV-LED emitting 350nm and vertical UV sensor with responsivity of 150 mA/W at 193nm on Si substrate.

AlGaAs/InGaAs HEMTs passivated with atomic layer deposited SiO 2 using aminosilane precursors

Atomic layer deposited SiO2 has been applied to AlGaAs/InGaAs high electron mobility transistors (HEMTs) for surface passivation employing bis(ethylmethylamino)silane (BEMAS) and tris(dimethylamino)silane (3DMAS). The BEMAS SiO2 HEMT has achieved a lower on-resistance, as compared to the 3DMAS. This suggests excellent termination of surface dangling bonds by BEMAS.

Excellent surface passivation of crystalline silicon by ternary Al x Mg 1−x O y thin films

A new class of passivation material, ternary Al_xMg_1-xO_y is developed and its surface passivation and interface properties on silicon surfaces are investigated in this study. Super-cycle plasma-enhanced atomic layer deposition is employed to fabricate Al_xMg_1-xO_y thin films and can effectively engineer physical properties of the thin films. Our study also shows that the developed Al_xMg_1-xO_y can provide excellent surface passivation on p-type silicon as indicated by very low S_eff,_max of ~1.8 cm/s after annealing. The observed excellent passivation quality seems to be due to enhanced interface properties (i.e. enhanced Q_eff and D_it) by Mg ion doping into AlO_x.

SiN x passivated GaN HEMT by plasma enhanced atomic layer deposition

Summary form only given. Plasma enhanced atomic layer deposited (PEALD) films of SiNx and Al2O3 have been investigated for surface passivation of AlGaN/GaN high electron mobility transistors (HEMTs). Through DC characterization of the fabricated HEMTs with the 3 nm thick films, the SiNx passivated HEMT showed the lowest on-resistance (Ron) of 6.7 Ω · mm. Since channel resistances under the gate electrodes and Ohmic contact resistances are identical to all the samples due to the same lots of fabrication, the lowest Ron is ascribed to the reduced channel resistance between gate and Ohmic electrodes where the film was deposited, i.e. an increase in the electron concentration at the channel region. This increase suggests lowering of the electron potential at the surface, and the lowering would be ascribed to a decrease in surface traps with electrons captured. Consequently, this implies that dangling bonds of the HEMT surface are well terminated by PEALD-SiNx.

InGaAs triangular barrier photodiodes for high-responsivity detection of near-infrared light

InGaAs triangular barrier (TB) structures of various barrier thicknesses have been formed on InP substrates. With them, we have fabricated TB photodiodes that yield a very high responsivity of 2.3 × 104 A/W at 100 K for the 1312 nm light of 320 fW power. By passivating the diode surface with polyimide, the dark current has been markedly reduced. Diodes with thicker barriers show higher sensitivity and responsivity, reflecting the enhancement of the barrier lowering effect by photogenerated holes.

Formation of conductive spontaneous via holes in AlN buffer layer on n+Si substrate by filling the vias with n-AlGaN by metal organic chemical vapor deposition and application to vertical deep ultraviolet photo-sensor

We have grown conductive aluminum nitride (AlN) layers using the spontaneous via holes formation technique on an n+-Si substrate for vertical-type device fabrication. The size and density of the via holes are controlled through the crystal growth conditions used for the layer, and this enables the conductance of the layer to be controlled. Using this technique, we demonstrate the fabrication of a vertical-type deep ultraviolet (DUV) photo-sensor. This technique opens up the possibility of fabrication of monolithically integrated on-chip DUV sensors and DUV light-emitting devices (LEDs), including amplifiers, controllers and other necessary functional circuits, on a Si substrate.

Novel Vertical AlGaN Deep Ultra Violet Photo–detector on n+Si Substrate using Spontaneous Via Holes Growth Technique

Vertical AlGaN deep ultra violet (DUV) photo-detector has been successfully fabricated on n+-Si substrate by spontaneous via holes growth. The spontaneous via holes turn the insulating AlN buffer layer to be conductive, which is indispensable for growing AlGaN epitaxial layer for device applications. By introducing spontaneous via holes, direct current flow from p-electrode to n+-Si substrate becomes possible. This vertical device is easily enlarged to realize large area solar-blind photo-detector which is necessary for many applications for sensing contamination of water, biological materials, and so on, under sunshine.