Yoshitsugu Yamamoto

Thermal stability of AlInAs/GaInAs/InP heterostructures

The origin of the thermal instability of the AlInAs/GaInAs system is identified and a novel method to recover the thermal degradation is also demonstrated. The thermal diffusion of fluorine into the Si‐doped AlInAs layer is found to be the main cause of the electrical deterioration of this system. This finding has led to a method to recover the thermal degradation by purging the fluorine off using the reannealing in the ultrahigh‐vacuum condition. This method is now potentially becoming a good candidate as a tip for the AlInAs/GaInAs devices fabrication including laser diode and high electron mobility transistor.

Degradation mechanism of the AlInAs/GaInAs high electron mobility transistor due to fluorine incorporation

The electrical degradation of AlInAs/GaInAs high electron mobility transistor (HEMT) due to the fluorine contamination is quantitatively explained through the comprehensive annealing experiments and bias‐temperature tests. The thermal degradation rate is found to be mainly determined by the following electrochemical reaction of fluorine with donor species after the quite fast diffusion of fluorine into the AlInAs layer. It is also confirmed that the thermal degradation is stringently affected by the electric field resulting in the one‐sided degradation near the anode. These findings are valuable knowledges in improving the reliability of AlInAs/GaInAs HEMT under the dc accelerated life test at high temperature.

A C-band AlGaN/GaN HEMT with Cat-CVD SiN passivation developed for an over 100 W operation

We applied a Cat-CVD (catalytic chemical vapor deposition) passivation film to AlGaN/GaN HEMTs, to resolve the trade-off between their drain current transient time and gate-drain break down voltage. We did not employ any field plate because it degrades high frequency operation over C-band. The SiN passivation film, deposited after a NH 3 treatment, resulted in less transient time and less gate leakage current than conventional PE-CVD passivation. A T-shaped gate HEMT fabricated by this technique, with Lg = 0.4 μm and Wg = 50.4 mm, delivered an output power over 140 W (2.79 W/mm), which was a record power at C-band.

Photovoltaic effects on Franz–Keldysh oscillations in photoreflectance spectra: Application to determination of surface Fermi level and surface recombination velocity in undoped GaAs∕n-type GaAs epitaxial layer structures

We demonstrate that the surface Fermi level and surface recombination velocity in undoped GaAs∕n-type GaAs (i-GaAs∕n-GaAs) epitaxial layer structures can be simultaneously estimated from Franz–Keldysh oscillations (FKOs) in photoreflectance spectra, taking account of the photovoltaic effects. Initially, we performed computational studies on the surface electric fields in i-GaAs∕n-GaAs structures under the illumination of a probe beam. The surface electric-field strength is sensitive to the surface Fermi level and surface recombination velocity. We have found that these parameters can be evaluated from the dependence of the surface electric-field strength on the probe-beam power density. Next, we estimated experimentally the surface Fermi level and surface recombination velocity in an as-grown i-GaAs∕n-GaAs structure by analyzing the photovoltaic effect on the FKOs. The period of the FKOs increases with a decrease in the probe-beam power density. The surface Fermi level and surface recombination velocity a...

Donor passivation in n-AlInAs layers by fluorine

The origin and mechanism for the thermal degradation of the n-AlInAs layer are discussed. The thermal degradation of carrier concentration and mobility is found to occur predominantly in the n-AlInAs layer, which is caused by annealing at a temperature less than 450/spl deg/C. The origin of the deterioration is ascertained to be the thermally diffused fluorine, which passivates donors in the n-AlInAs layer. As the electronegativity of the fluorine atom is the largest among the elements, and the atomic radius of fluorine atom is considerably small enough to pass through the crystal, fluorine atoms are reasonably thought to diffuse into the n-AlInAs layer then react with the free electrons, which results in the F/sup -/ scattering centers (F/sup -/: ionized fluorine).

Alloyed and Non-Alloyed Ohmic Contacts for AlInAs/ InGaAs High Electron Mobility Transistors

AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.

Second harmonic generation from thermally poled CdS microcrystal-containing glasses

The alkali borosilicate glasses containing CdS as a constituent were heat-treated or thermally poled to prepare CdS microcrystal-containing glasses. Second harmonic generation (SHG) from these glasses was measured, and the effects of the applied voltage on the crystallization behavior and SHG intensity were discussed. In poled glass samples, wurtzite type CdS microcrystals were precipitated at lower temperature than in unpoled ones. It was considered that the applied electric field affected the crystallization behavior of CdS crystals through the increase of temperature of the glass sample and migration of S2− ions. The poled sample showed larger SHG intensity than the sample merely heat-treated, which was explained in terms of modification structure and orientation of precipitated CdS microcrystals.

Fluorine limited reliability of AlInAs/InGaAs high electron mobility transistors with molybdenum gates

A highly reliable AlInAs/InGaAs high electron mobility transistor with the projected lifetime of 10/sup 6/ hours at 125/spl deg/C is developed. The gate electrode sinking is eliminated by adopting molybdenum gate contact metal, and the carrier passivation is controlled by eliminating the extrinsic fluorine containing processes. The experimental results and theoretical calculation indicate the present reliability is limited by the intrinsic fluorine contamination from the air.

Manufacturability and reliability of InP HEMTs

Abstract This article describes the present status concerning manufacturability and reliability of InP HEMTs ( n -AlInAs/InGaAs/InP HEMTs) towards the practical use. The precise and reproducible control in the gate recess etching for the InP HEMTs was realized by employing the highly selective pH-adjusted citric acid based solution. The 0.15 μm-length T shaped gate InP HEMT fabricated on 3 inch wafers by the selective recess etching showed a minimum noise figure as low as 0.9 dB with an associated gain of 7.0 dB at 60 GHz and a standard deviation in I dss as low as 3.2 mA. These successful results promise the good manufacturability of the excellent performance InP HEMTs with high yield. The present reliability of the InP HEMTs is at least one order lower than that of conventional GaAs based HEMTs because of their poor thermal stability. It is demonstrated that the main reason for the thermal instability of the InP HEMTs originates from the donor passivation in the n -AlInAs electron supplying layer caused by fluorine during the thermal stress and that this donor passivation is peculiar to the materials containing both AlAs and InAs. The mechanism of this peculiar donor passivation and some ideas for the suppression of it is discussed.

A super low noise V-band AlInAs/InGaAs HEMT processed by selective wet gate recess etching

A 0.15 /spl mu/m T-shaped gate AlInAs/InGaAs high electron mobility transistor (HEMT) with excellent RF performances has been developed using a selective wet gate recess etching. An extremely low minimum noise figure (Fmin) of 0.9 dB with an associated gain (Ga) of 7.0 dB has been achieved at 60 GHz for a SiON-passivated device. This is the lowest value of Fmin ever reported for AlInAs/InGaAs HEMT with a passivation film.<<ETX>>