D. L. Miller

Carbon doping of GaAs and (In,Ga)As in solid source molecular beam epitaxy using carbon tetrabromide

We have grown C‐doped GaAs and (In,Ga)As epitaxial layers of device quality in a standard solid source molecular beam epitaxy system using carbon tetrabromide (CBr4) as the carbon source. Dopant incorporation was relatively efficient for both GaAs and (In,Ga)As, requiring a CBr4 beam pressure of about 1×10−6 Torr to achieve a hole density of 1.5×1020/cm3. For doping in the 1019/cm3 range, hole mobilities were comparable to or slightly higher than those of Be‐doped layers with the same carrier concentrations. Modulation‐doped structures grown immediately after heavily C‐doped GaAs layers exhibited reduced two‐dimensional electron gas mobility, but the mobility recovered to previous values within 24 h. (Al,Ga)As/GaAs heterojunction bipolar transistors (emitter size=25 μm×50 μm) with C‐doped bases (p=1.2×1019 cm−3) had common emitter small signal current gains averaging 86 at an emitter current density of 970 A/cm2. The relatively low gas load during growth, the lack of long‐term memory effect, and the accep...

Unique determination of AlGaAs/GaAs HBT's small-signal equivalent circuit parameters

A new parameter extraction technique for heterojunction bipolar transistors (HBTs) is described. Utilizing a novel low frequency extraction algorithm, the intrinsic elements and the resistive parasitics are obtained. The overall small-signal equivalent circuit of HBTs is then determined based on those extracted element values. This technique advances current equivalent circuit modeling capability of HBTs by minimizing the interactive computer optimization/simulation process and removing the need of special test structures.<<ETX>>

Nearly isotropic etching of 6H‐SiC in NF3 and O2 using a remote plasma

Nearly isotropic etching of the 6H‐SiC carbon face has been achieved in a remote plasma at 330 °C using a mixture of O2 and NF3 in argon. Using evaporated aluminum as a mask, undercutting has been observed to a distance equal to the etch depth. The etch rate is a function of the ratio of O2 to NF3 flow rates and of temperature, peaking strongly to 220 nm/min at 82% oxygen for 330 °C. Smooth surfaces were obtained for gas ratios leading to the maximum etch rate, and also for a NF3‐argon mixture, with significant roughening observed for other O2‐NF3‐argon mixtures. In the absence of a practical wet etch for SiC, this procedure is promising for isotropic etching in SiC device processing.

Evolution of the GaAs(001) surface structure during the transition from the As-rich (2×4) to the Ga-rich (4×2) reconstruction

Abstract Evolution of the GaAs(001) surface during the transition from the As-rich (2×4) to the Ga-rich (4×2) reconstruction has been studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). It has been found that the (2×4)–(4×2) transition proceeds via the formation of intermediate phases exhibiting (3×6) and (4×6) LEED patterns. STM images indicate that these phases are multi-domain. In particular, the (3×6) phase is locally composed of domains of the “(2×6)” and disordered phases, while the (4×6) phase in addition contains (4×2) domains. To explain STM images taken in a dual polarity bias mode, structural models for the “(2×6)” and disordered phases are proposed. These structures are electrostatically compensated via disorder of As (“2×6” phase) and Ga (disordered phase) dimers. A comprehensive picture of the (2×4)–(4×2) phase transition based on the analysis of the STM data is presented.

Capacitance spectroscopy of InAs self-assembled quantum dots embedded in a GaAs/AlAs superlattice

The characteristics of the InAs self-assembled quantum dots embedded both in a GaAs bulk matrix and in a GaAs/AlAs superlattice were investigated. Evidences of electrons confinement inside the InAs quantum dots were obtained using both capacitance–voltage measurements and Raman spectroscopy. A much stronger electron localization was detected for the quantum dots embedded in the superlattice in comparison with those embedded in bulk GaAs. As a consequence, the electrical characteristics of the structures with quantum dots grown in superlattices were found to be significantly thermo-stabilized. The origins of these effects are discussed in connection with the differences between the electronic features of the two kinds of structures.

Carbon doping of InGaAs in solid‐source molecular beam epitaxy using carbon tetrabromide

Carbon tetrabromide was used to dope (In,Ga)As layers lattice matched to InP grown by solid‐source molecular beam epitaxy. The maximum hole density depended on substrate temperature. A hole concentration as high as 7.5×1019 cm−3 was achieved at a substrate temperature of 450 °C with reduced As2 flux. Variations in arsenic flux intensity were found to have little effect on the doping density. Hole mobility was comparable to the mobility of Be‐doped material grown in our MBE system and to the mobility of CCl4‐doped material grown elsewhere. We observed a short‐term doping memory effect which we attribute to desorption of CBr4 from growth chamber internal surfaces due to radiant heat from column III ovens. (In,Al)As/(In,Ga)As Npn heterojunction bipolar transistors fabricated using CBr4 doping for the (In,Ga)As base layer with p=2×1019 cm−3 exhibited a dc current gain of eight.

Demonstration of a GaAs-based compliant substrate using wafer bonding and substrate removal techniques

A GaAs-based compliant substrate that uses an intermediate AlGaAs-oxide layer to separate thin 150 /spl Aring/-1000 A GaAs compliant layers from a GaAs host substrate is described. The compliant substrates and epitaxial layers of lattice-mismatched In/sub 0.15/Ga/sub 0.85/As were studied using atomic force microscopy and double-crystal X-ray diffraction. The surface morphology of the 1000 A compliant substrate prior to growth had an RMS and peak-to-peak roughness of 10 /spl Aring/ and 100 /spl Aring/. Following growth of 3000 /spl Aring/ In/sub 0.15/Ga/sub 0.85/ the root mean square (RMS) roughness increased to 50 /spl Aring/, and slip lines were observed in the [110] direction. A comparison of lattice-matched p/sup +/-n junction diodes grown on a substrate with a 1000 /spl Aring/ compliant layer and a standard GaAs substrate revealed similar dark current-voltage characteristics, which demonstrate the high quality of the compliant substrate.

Molar fraction and substrate orientation effects on carbon doping in InGaAs grown by solid source molecular beam epitaxy using carbon tetrabromide

Carbon incorporation in InGaAs and GaAs is systematically studied in solid-source molecular beam epitaxy (MBE) as a function of carbon tetrabromide pressure, indium molar fraction, and substrate orientation. The maximum attainable free carrier concentration in GaAs and InGaAs lattice matched with InP was 2×1020 cm−3. The etching effect of CBr4 on growth rate reduction, surface morphology, and growth mechanism is clarified. A comparative study of carbon incorporation as function of substrate orientation and polarity was undertaken by the growth of GaAs and In0.53Ga0.47As on (n11)A and B (n=2, 3, 5) and (100) oriented substrates. Free carrier concentration and mobility measurements showed no carbon autocompensation in GaAs but strong amphoteric behavior for In0.53Ga0.47As grown on arsenic terminated planes. Measurement of hole concentration as function of indium molar fraction in InxGa1−xAs shows that carbon tetrabromide can be used as an effective acceptor doping percursor for indium molar fraction x less ...

Luminescence from GaAs(100) surface excited by a scanning tunneling microscope

We have measured luminescence of atomically clean GaAs(100) samples induced by a scanning tunneling microscope (STM) under ultrahigh vacuum (UHV) conditions. GaAs(100) samples were grown by molecular beam epitaxy and capped with a thick arsenic overlayer to protect the surface during transfer through ambient atmosphere to the UHV STM chamber equipped with a light collection system. The luminescence arises from the radiative recombination of the excited carriers across the band gap induced by the tunneling current. Maps of luminescence as a function of lateral position of the STM tip (photon maps) have been recorded. Arsenic related features of the size of ∼20 nm appear as dark areas in the photon maps indicating increased local nonradiative recombination. Photon maps acquired at positive and negative sample bias show significant differences in contrast. Mechanisms responsible for the STM excited luminescence and contrast observed in the photon maps are discussed.

Analysis of charge-compensating defects on the GaAs(111)B(2 × 2) surface

Abstract We present an analysis of defects on the GaAs(111)B-(2 × 2) surface, as revealed by STM. Defects are formed at the intersections of the boundaries of domains of As trimers. The brightness varies around these defects in the empty-state image. We present model atomic structures of these defects and analyze how they are charged. We find five kinds of acceptor defects and one kind of donor defect. The charges associated with these defects are suggested to be responsible for the variation in the brightness, i.e., the tunneling probability. It is proposed that these defects result in pinning of the surface Fermi-level at midgap, similar to recently observed kink defects in missing dimer rows on the GaAs(001)-(2 × 4) surface. The total net charge of the surface defects equals the space charge within the depletion region, in agreement with a defect-induced surface Fermi-level pinning mechanism.