Kohji Matsumura

A New High Electron Mobility Transistor (HEMT) Structure with a Narrow Quantum Well Formed by Inserting a Few Monolayers in the Channel

A new HEMT wafer has been developed whose channel layer has a narrow bandgap semiconductor with a few monolayers inserted at an optimum position in the channel, namely, the point where the probability density of electrons is maximum in the lowest subband and negligible in the first excited subband. The Al0.22Ga0.78As/In0.15Ga0.85As pseudomorphic HEMT wafer with one InAs monolayer inserted at the optimum position has provided Hall electron mobility increments nearly 15% higher at 300 K and 20% higher at 77 K than those of conventional pseudomorphic HEMT wafers.

A new two-mode channel FET (TMT) for super-low-noise and high-power applications

A super-low-noise two-mode channel FET (TMT) with high- and plateau-shaped transconductance (g/sub m/) characteristics has been developed. It has two electron transport modes against the applied gate voltage (V/sub gs/). That is, the electrons mainly drift in a highly doped channel region at a shallow V/sub gs/. A plateau g/sub m/ region and the maximum g/sub m/ were achieved at a V/sub gs/ range of -0.25 approximately +0.5 V and 535 mS/mm, respectively. The minimum noise figure and associated gain for the TMT were superior in the low-drain-current (I/sub ds/) region and nearly equal in the middle and high I/sub ds/ region to those of an AlGaAs/InGaAs pseudomorphic HEMT fabricated using the same wafer process and device geometry.<<ETX>>

Influence of rapid thermal annealing on modulation doped structures

Abstract We have investigated the influence of high temperature annealing on modulation doped structures of AlGaAs/GaAs, AlGaAs/InGaAs and InAlAs/InGaAs systems grown by molecular beam epitaxy. Hall-measurement reveals reduction in two-dimensional electron gas mobility and almost unchanged sheet density after annealing at 800–880°C for 5 s in each hetero-junction system. The mobility reduction is enhanced with the increase in annealing temperature and with the decrease in thickness of a spacer between a donor layer and a channel layer. This behavior is attributed to diffusion of Si dopants from a donor layer to a spacer layer resulting in an increasing ionized impurity scattering effect. It is found that In contained structures especially an InP-based InAlAs/InGaAs structure, provide both large 2DEG sheet density and excellent thermal stability of the modulation doped structure.

Quantification of Electrical Deactivation by Triply Negative Charged Ga Vacancies in Highly Doped Thin GaAs Layers.

We present for the first time a theoretical approach to electrical deactivation by triply negative charged Ga vacancies (V 3- Ga in highly doped thin n-GaAs layers grown by molecular beam epitaxy, and quantify their deactivation under as-grown and annealed conditions. We also show that thinning of n-GaAs epitaxial layers results in low-level electrical deactivation. This effect is apparently caused by the fact that thinning of the doped layers results in lowering of the Fermi energy in the doped layers, and thereby inhibition of the generation of V 3- Ga acceptors. Furthermore, we deduce from the results of this study the thermal equilibrium concentration of V 3- Ga in intrinsic GaAs. The resulting expression is [V 3- Ga (i)] = 5.37 X 10 31 exp(-4.64eV/k B T) cm -3 .

Excellent Thermally Stable Epitaxial Channel for Implanted Planar-Type Heterojunction Field-Effect Transistors

We demonstrate for the first time that the decrease in the carrier concentration of highly doped GaAs layers caused by annealing is alleviated by thinning the layers. It is also suggested that the decrease is dependent on the Fermi energy in the doped layers. Thermally stable thin Si-doped GaAs channels are formed in implanted planar-type two-mode channel field-effect transistors (P-TMTs). A 0.2-μm device having a GaAs channel 9 nm thick with a doping level of 7 x 10 18 cm -3 exhibits excellent performance, such as a transconductance g m of 450 mS/mm, a current-gain cutoff frequency f T of 72 GHz, and a maximum frequency of oscillation f max of 140 GHz. Furthermore, it is indicated that highly doped thin layers are very effective for improving the DC and microwave performance of P-TMTs.

Relationship between Low-Noise Performance and Electron Confinement in the Channel of Two-Mode Channel Field-Effect Transistors in a Low-Drain-Current Condition

We investigated the relationship between the minimum noise figure (NF min) and electron confinement in the channel of the two-mode channel field-effect transistor (TMT) which we developed previously, by comparing the TMT and an AlGaAs/InGaAs pseudomorphic high electron mobility transistor (P-HEMT) with a 10 nm InGaAs channel layer. The TMT had a superior measured NF min and stronger electron confinement in a low-drain-current (I ds) bias condition than the P-HEMT. The superior measured NF min of the TMT resulted in a smaller fitting factor (K f) in Fukuis noise equation than that of the P-HEMT. We demonstrated that the stronger electron confinement of the TMT leads to an increase in the correlation coefficient between drain noise current and gate-induced noise current and results in a smaller K f, which plays an important role in the reduction of NF min.

Doping profile control and two‐dimensional electron gas formation by Si diffusion into III‐V compounds

The doping characteristics of Si‐diffused III‐V compounds have been investigated using fully dielectric diffusion sources consisting of undoped SiOx/SiN double‐layered films prepared by plasma‐enhanced chemical‐vapor deposition. It is demonstrated that the rectangular‐shaped carrier concentration profiles resulting from the Si diffusion in GaAs can be controlled by varying the deposition parameters of the SiOx/SiN films, i.e., the N2O flow rate in the SiOx deposition, the SiOx film thickness, and the NH3 flow rate in the SiN deposition. It is explained that the profile variations are determined by the quantity of an excess of Si in the SiOx bottom film and the outdiffusion rate of Ga and/or As from GaAs. Furthermore, the Si diffusion experiments are carried out in AlxGa1−xAs, and the formation of a two‐dimensional electron gas with a Hall mobility of 5060 cm2/V s at 300 K and 97 500 cm2/V s at 77 K is achieved by diffusing Si into an undoped GaAs/Al0.22Ga0.78As heterostructure.