Yui Nishio

Comparison between theoretical and experimental results for energy states of two-dimensional electron gas in pseudomorphically strained InAs high-electron-mobility transistors

The energy states of a two-dimensional electron gas (2DEG) in high-electron-mobility transistors with a pseudomorphically strained InAs channel (PHEMTs) were analyzed rigorously using a recently established theory that takes into account the nonparabolicity of the conduction band of the channel layer. The sheet density of the 2DEG in InxGa1−xAs-PHEMTs and the drain I–V characteristics of those devices were calculated theoretically and compared with the density and characteristics obtained experimentally. Not only the calculated threshold voltage (VTH) but also the calculated transconductance agreed fairly well with the corresponding values obtained experimentally. When the effects of the compositions of the InxGa1−xAs subchannel layer in the composite channel and the channel layer on energy states of 2DEG were investigated in order to establish a guiding principle for a design of the channel structure in PHEMTs, it was found that VTH is determined by the effective conduction-band offset energy ΔEC between the InAlAs barrier and the channel layers.

Analysis of energy states of two-dimensional electron gas in pseudomorphically strained InSb high-electron-mobility transistors taking into account the nonparabolicity of the conduction band

We propose a high electron mobility transistor with a pseudomorphically strained InSb channel (InSb-PHEMT) having an InSb composite channel layer in which the Al y In1− y Sb sub-channel layer is inserted between the InSb channel and the Al x In1− x Sb barrier layers to increase the conduction-band offset (ΔE C) at the heterointerface between the InSb channel and the Al x In1− x Sb barrier layers. The energy states for the proposed InSb-PHEMTs are calculated using our analytical method, taking account of the nonparabolicity of the conduction band. For the proposed InSb-PHEMTs, putting the sub-channel layers into the channel is found to be effective for obtaining a sufficiently large ΔE C (~0.563 eV) to restrain electrons in the channel and increase the sheet concentration of two-dimensional electron gas to as high as 2.5 × 1012 cm−2, which is comparable to that of InAs-PHEMTs. This also leads to a large transconductance of PHEMTs. In the proposed InSb-PHEMTs, electrons are strongly bound to the channel layer compared with InAs-PHEMTs, despite the effective mass at the conduction band (0.0139 m 0) of InSb being smaller than that of InAs and ΔE C for the InSb-PHEMTs being 25% smaller than that for the InAs-PHEMTs. This is because the bandgap energy of InSb is about one-half that of InAs, and hence, the nonparabolicity parameter of InSb is about twice as large as that of InAs.

Analysis of energy states where electrons and holes coexist in pseudomorphically strained InAs high-electron-mobility transistors

In strained high-electron-mobility transistors (HEMTs) with InAs as the channel, excess electrons and holes are generated in the drain region by impact ionization. In the source region, electrons are injected to recombine with accumulated holes by the Auger process. This causes the shift of the gate potential, V GS,shift, for HEMTs. For a system where electrons and holes coexist, we established a theory taking into account the nonparabolicity of the conduction band in the InAs channel. This theory enables us to rigorously determine not only the energy states and the concentration profiles for both carriers but also the V GS,shift due to an accumulation of holes. We have derived the Auger recombination theory which takes into account the Fermi–Dirac statistics and is applicable to an arbitrary shape of potential energy. The Auger recombination lifetime τA for InAs-PHEMTs was estimated as a function of the sheet hole concentration, p s, and τA was on the order of psec for p s exceeding 1012 cm−2.

Comparison between theoretical and experimental results for energy states of two-dimensional electron gas in pseudomorphically strained InAs-HEMTs

Comparison between theoretical and experimental results for energy states of the two-dimensional electron gas has been made for pseudomorphically strained InAs-HEMTs. Not only the threshold voltage but the transconductance of HEMTs calculated using the non-parabolic energy band model agreed fairly well with those obtained experimentally. In addition, the effect of composition of the InxGa1-xAs barrier layer on energy states of 2DEG was investigated. It was found that VTH does not depend on the structure of the buffer layer used.

Theoretical study of energy states of two-dimensional electron gas in pseudomorphically strained InAs HEMTs taking into account the non-parabolicity of the conduction band

We determined rigorously the energy states of a two-dimensional electron gas (2DEG) in high electron mobility transistors (HEMTs) with a pseudomorphically strained InAs channel (InAs PHEMTs) taking into account the non-parabolicity of the conduction band for InAs. The sheet carrier concentration of 2DEG for the non-parabolic energy band was about 50% larger than that for the parabolic energy band and most of the electrons are confined strongly in the InAs layer. In addition, the threshold voltage for InAs PHEMTs was about 0.21 V lower than that for conventional InGaAs HEMTs.