MBE growth and characterization of MODFET heterostructures using pseudomorphic InGaAs or InAs/GaAs superlattice channels

We studied the influence of the growth temperature Ts and of the InGaAs quantum-well channel thickness dch on the 300 and 77 K Hall electrical properties of pseudomorphic MODFET-type heterostructures grown by molecular-beam epitaxy (MBE). In agreement with Nguyen et al., we find an optimum channel thickness of 90 Å for an indium composition y = 0.25 of the channel. Significant improvements in sheet resistivity ϱs and in carrier concentration nso were obtained by using AlGaAs doped barriers on both sides of the pseudomorphic channel. We were thus able to obtain a 2DEG sheet density nso as high as 4.0×1012 cm-2 at 77 K, which is among the highest values reported for MODFET's on GaAs. Promising results were obtained on MODFET's using an (InAs)m (GaAs)n short period superlattice for the channel

A correlation between surface morphology and RHEED intensity variation for growth of GaAs by molecular beam epitaxy

We present a correlation between the behaviour of the RHEED specular reflected beam intensity during the initial phases of growth, the MBE growth conditions (T(s), P(As4), V(GaAs)), and the surface morphology examined by Nomarski contrast microscopy after the growth of a 2-mu-m GaAs layer on (001) GaAs substrates. The quality of the layers was also checked by low-temperature photoluminescence. We found that the steady-state intensity of the reflected beam gives a direct indication of the smoothness of the growth surface. From the RHEED pattern comparison we obtained: (i) for a fixed growth temperature and V/III beam equivalent pressure (BEP) ratio, a lower growth rate leads to smoother surfaces; (ii) at a fixed growth temperature and growth rate, there is an optimum As4 pressure which gives the maximum number of oscillations that can be observed before reaching a steady-state intensity. This optimum As4 pressure induces a minimum surface roughness and a high low-temperature photoluminescence (PL) intensity. Low-temperature photoluminescence measurements showed that the growth at 585-degrees-C instead of 620-degrees-C or at greater BEP V/III ratio, leads to higher incorporation of shallow impurities

Photo-Hall studies of modulation-doped field-effect trasistor heterostructures using (InAs)m(GaAs)n superlattice channels

We studied the electrical properties, the Hall mobility and the free carrier concentration of modulation-doped field-effect transitor heterostructures using M(InAs)mN(GaAs)m short-period superlattice (SPS) channels. We changed the number of monolayers m for InAs, n for GaAs and the numbers M and N of interfaces InAsmGaAsn in the channel. In the SPS, the thickness of the InAs layer was varied from 0.5 ± 0.1 to 1.6 ± 0.1 monolayers (ML) and that of GaAs from 5 to 15 ML. The number M of interfaces varied from 3 to 7 while the number N varied from 2 to 6. The total SPS channel thickness was varied, but always kept below the critical layer thickness calculated from the double kink model derived by Matthews and Blakeslee. The persistent photoconductivity effect, at 77 K, was employed to study the variation of the Hall mobility and free carrier density in the SPS channels. A red light-emitting diode was used as the illumination source. Our results indicate that the Hall mobility increases for (a) a decreasing number of InAsGaAs and GaAsInAs interfaces, (b) on employing an integral number of InAs monolayers, and (c) on employing an increasing number of GaAs monolayers. We believe that they are effective in producing surface smoothing

Photoluminescence from the 2D electron-gas and many-body effects as a probe of the crystalline quality of pseudomorphic GaAs/InGaAs/AlGaAs and GaAs/n(GaAs)10(n+1)(InAs)m/AlGaAs MODFETs

We have performed low temperature (5K) photoluminescence (PL) measurements in order to study the crystalline quality of pseudomorphic modulation-doped field effect transistors (MODFET's) grown by MBE. MODFET's based on GaAs/AlGaAs with either an InGaAs or a (GaAs)n(InAs)m short period superlattice (SPS) channel have been studied. On modulation doped structures, the presence of free carriers into the channel strongly affects the PL emission,. In this paper, we present a study of PL line shape of MODFET structures with different channel thicknesses and growth conditions. A correlation between the PL line shape and these parameters is clearly observed

Extraction of FET parameters at low drain bias by taking into account the dependence of mobility on 2D electron gas concentration

An original method for the extraction of FET parameters at low drain bias is presented. It is based on a simple linear charge-control model and on a power-law dependence (with an exponent k > 0 for GaAs/AlGaAs MODFET's and k < 0 for Si-MOSFET's) of the low-field mobility-mu on the two-dimensional electron gas (2DEG) concentration n(S), valid in a certain range of gate voltages. Simple analytical expressions for the transfer characteristics I(ds)-V(gs) and g(m)-V(gs) at low drain bias are combined to extract reliable values of the threshold voltage Vt, the power exponent k, the total parasitic series resistance (R(s)+R(d) and an important control parameter-beta'. We verified that the values of beta' and k extracted on a test MODFET at 300 and 77 K agree very well with those deduced directly from Hall measurements on gated Hall-bridge structures. Our analysis is also applied to extract MOSFET parameters at room temperature