Room Temperature Hall Mobility Research Articles

Growth of gallium nitride by hydride vapor-phase epitaxy

This paper reviews the growth of GaN thick films by hydride vapor-phase epitaxy (HVPE). Emphasis is placed on recent developments, including the growth of nondegenerate material, characterization of film properties and suitability of such films for epitaxial device overgrowths. Films up to 74 μm thick have been deposited on sapphire substrates with no evidence of thermally induced cracking and a room-temperature Hall mobility of 880 cm 2/V s at 293 K. Dislocation densities have been found to decrease with film thickness to 5 × 10 7 cm −2 for a 40 μm thick sample. Epitaxial films overgrown on these HVPE GaN buffers, both by organometallic vapor-phase epitaxy and molecular-beam epitaxy, replicate the defect structure of the HVPE buffer, resulting in dislocation densities no higher than the HVPE buffer and lower than are typically observed for nitride epilayers grown on other substrate materials. Efforts towards film/substrate separation will be discussed.

Photoconductive decay in LCVD/PECVD low temperature grown GaN

Photoconductive decay in undoped GaN has been investigated at room temperature using an ArF excimer laser as illuminative source and a boxcar integrator for detection of decay signals. GaN films were grown by combined laser and microwave plasma enhanced chemical vapour deposition at 550°C. The respective room temperature electron concentration and Hall mobility of the films were measured to be in the range 10 15–10 16 cm −3 and up to 200 cm 2/V s. Two time constants, 0.8 and 6 μs, are distinguishable in typical photoconductive decay curves and are associated with a dominant fast recombination and a weaker, slower process via an unidentified defect state respectively. Near-band photoluminescence dominates the emission spectrum with little contribution from the sub-bandgap process often found in the presence of high-density defects.

Hall mobility analysis in low-temperature-grown molecular-beam epitaxial GaAs

Temperature dependent conductivity and Hall effect measurements were carried out on molecular-beam epitaxial GaAs layers grown at 200–420 °C and separated from the substrate. An analysis of experimental data with and without considering the hopping Hall mobility was made. An extremely low room temperature Hall mobility of 0.14 cm2 V−1 s−1 was measured in the 250 °C layer, which could be interpreted as the hopping Hall mobility. The room temperature band Hall mobility (μHb) increases from 500 to 6000 cm2 V−1 s−1 and the power (n) of the temperature dependence of μHb (∼T−n) increases from 0.5 to 1.2 with increasing growth temperature from 300 to 420 °C.

Properties of single crystalline semiconducting CoSb3

A study of the thermoelectric properties of the skutterudite compound CoSb3 was carried out on single crystals grown by the Bridgman gradient freeze technique. p- and n-type samples were obtained over a wide range of carrier concentration. Undoped As-grown crystals show p-type conductivity while n-type samples were obtained by addition of Te or Pd. Samples were characterized by x-ray diffractometry, electron microprobe analysis, and density measurements. The physical properties of CoSb3 such as linear thermal expansion coefficient, sound velocity, and Debye temperature were also determined and are presented. Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect measurements were performed between room temperature and about 900 K. Exceptionally high Hall mobilities were obtained on p-type samples with a maximum room-temperature Hall mobility of 3300 cm2 V−1 s−1 at a carrier concentration of 1×1017 cm−3. The results of the transport property measurements are discussed and are in agreement with some recent predictions based on band structure calculations. The potential of CoSb3 for thermoelectric applications is evaluated.

Preparation and properties of thin polycrystalline MnSi 1.73 films

Thin MnSi 1.73 films were prepared by a DC sputter method in a high vacuum deposition chamber. As target material a MnSi 2 silicide target was used. Films were deposited onto quartz substrates at different temperatures (330–875 K) without any annealing steps after the sputter process. The composition of the samples was determined by Rutherford backscattering spectroscopy. Within the detection limit of this method no contamination in the films was found. The crystalline structure of the films was analyzed by transmission electron microscopy. At substrate temperatures of 530 K always a tetragonal crystalline phase of MnSi 1.73 was observed. The specific resistivity and the Hall mobility of the samples were determined in the temperature range from 300 to 25 K. The results of the electrical measurements verify the low crystallization temperature of the films. The character of the electrical transport in the crystalline films is strongly influenced by the preparation temperature. With rising substrate temperature the sign of the temperature coefficient of resistivity at room temperature changes from negative to positive values. At room temperature Hall mobilities in the region of 1.4 cm 2 V −1 s −1 were obtained. The temperature dependence of the electrical transport properties can be interpreted in the picture of a degenerated semiconductor. With optical measurements at room temperature an indirect gap of 0.46 eV was determined. The structure of the transmission spectra was influenced by the different heat treatments in the sample preparation.

Microwave plasma assisted LCVD growth and characterization of GaN

Gallium nitride films have been grown by microwave plasma assisted laser induced chemical vapor deposition at about 550°C. Trimethylgallium and ammonia served as group II and group V sources, respectively. Ammonia was introduced into the reaction chamber by two separate lines. In one of the lines, ammonia first passed through a microwave cavity where it could be ionized into a plasma, before being delivered to the chamber. An ArF excimer laser (193 nm) was used to photodissociate the ammonia and trimethylgallium introduced through the other line. The room temperature electron concentration and Hall mobility of the films were measured to be in the range 10 15–10 16 cm −3 and up to 200 cm 2/Vs, respectively. Strong room temperature near-band photoluminescence detected from the films indicated their good optical quality. The photoconductive decay of photocarriers was also investigated.

InP-based heterostructure field-effect transistors with high-quality short-period (InAs) 3 m/(GaAs) 1 m superlattice channel layers

InP-based heterostructure field-effect transistors (HFETs) incorporating an (InAs) 3 m /(GaAs) 1 m short-period superlattice (SPSL) subchannel are compared to HFETs using a ternary In 0.77Ga 0.23As alloy with respect to transport and device performance. Room temperature Hall mobility of 13100 cm 2/ V · s was measured on a (InAs) 3/(GaAs) 1 SPSL with a two-dimensional electron sheet density of 3.1 × 10 12 cm −2, which are the highest mobilities in such a material system so far. Sheet resistances as low as 35 Ω □ at 17 K confirm the high quality of the (InAs) 3/(GaAs) 1 SPSL channel material resulting in high transit and unilateral gain cut-off frequencies of 63 and 190 GHz, respectively, in HFETs exhibiting gate lengths of 0.65 μm. Nevertheless, a significant improvement compared to the ternary alloy could not be verified.

Diamond devices and electrical properties

Diamond offers tremendous potential for electronic applications such as field effect transistors. An investigation of the electrical properties of boron-doped homoepitaxial diamond films and the metal-oxide-diamond gate structure was performed. Additionally, field effect transistors were fabricated and characterized. Improvements in the diamond deposition process produced boron-doped homoepitaxial diamond films where the room temperature Hall mobility exceeded 1000 cm2 V−1 s−1. Analysis of the temperature-dependent carrier concentration indicated that the compensation was < 3 × 1015cm−3. The gate structure for metal-silicon dioxide-boron-doped diamond field effect transistors was evaluated by current-voltage and capacitance voltage measurements. Good correlation of the uncompensated acceptor concentration, determined by capacitance-voltage measurements, and the boron concentration, determined by secondary ion mass spectroscopy, was attained. Preliminary measurements suggested that the density of interface states for this structure was ≈ 1012 cm−2 eV−1. Field effect transistors exhibited saturation and pinch-off at temperatures as high as 773 K. The highest normalized transconductance measured was 1.3 mS mm−1. The field effect transistors were combined into analogue and digital circuits that operated at 523 K and 673 K, respectively.

Hydrogen incorporation into Si-doped InP deposited by gas-source molecular beam epitaxy

Hydrogen incorporation into Si-doped InP grown by gas-source molecular beam epitaxy was studied. P-H sites were identified by infrared spectroscopy. Proton-implanted reference samples were used to quantify the infrared results. Approximately 0.1 at. % hydrogen was found to be incorporated into InP:Si. Hall measurements indicated that most of the Si atoms were electrically active as donors. Rapid thermal annealing at 600 °C removed most of the bonded hydrogen from the samples. However, this resulted in relatively little change in either the room-temperature free-carrier concentration or Hall mobility.

Optoelectronic and Structural Properties of High-Quality GaN Grown by Hydride Vapor Phase Epitaxy

ABSTRACTGallium nitride (GaN) films have been grown by hydride vapor phase epitaxy (HVPE) in a vertical reactor design. We report on GaN growth directly on sapphire using a GaCl surface pretreatment. The electrical properties of these films compare favorably with the highest values reported in the literature for GaN. Specifically, a room temperature Hall mobility as high as 540 cm2 /V-s, with a corresponding carrier concentration of 2×1017 cm−3, have been attained. Additionally, the vesical reactor design has assisted in reducing nonuniformities in both film thickness as well as in transport properties due to depletion effects, as compared with horizontal designs. The dislocation density in these films has been determined by plan-view transmission electron microscopy to be ∼3×l08 cm−2 .Photoluminescence spectra obtained at 2 K show intense, sharp, near-bandedge emission with minimal deep level emissions. Stimulated emission has been observed in these films, utilizing a nitrogen laser pump source (λ=337.1 nm) with a threshold pump power of ∼0.5 MW/cm2 . These results suggest that HVPE is viable for the growth of high-quality nitride films, particularly for the subsequent homoepitaxial overgrowth of device structures by other growth methods such as OMVPE and MBE.

Detailed analysis of carrier transport in InAs0.3Sb0.7 layers grown on GaAs substrates by metalorganic chemical-vapor deposition

InAs0.3Sb0.7 layers with mirrorlike morphology have been grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. A room-temperature electron Hall mobility of 2×104 cm2/V s has been obtained for a 2-μm-thick layer. Low-temperature resistivity of the layers depended on TMIn flow rate and layer thickness. Hall mobility decreased monotonically with decreasing temperature below 300 K. A 77 K conductivity profile has shown an anomalous increase in the sample conductivity with decreasing thickness except in the near vicinity of the heterointerface. In order to interpret the experimental data, the effects of different scattering mechanisms on carrier mobility have been calculated, and the influences of the lattice mismatch and surface conduction on the Hall measurements have been investigated by applying a three-layer Hall-effect model. Experimental and theoretical results suggest that the combined effects of the dislocations generated by the large lattice mismatch and strong surface inversion may lead to deceptive Hall measurements by reflecting typical n-type behavior for a p-type sample, and the measured carrier concentration may considerably be affected by the surface conduction up to near room temperature. A quantitative analysis of dislocation scattering has shown significant degradation in electron mobility for dislocation densities above 107 cm−2. The effects of dislocation scattering on hole mobility have been found to be less severe. It has also been observed that there is a critical epilayer thickness (∼1 μm) below which the surface electron mobility is limited by dislocation scattering.

Anomalous Hall effect in InSb layers grown by metalorganic chemical vapor deposition on GaAs substrates

InSb epitaxial layers have been grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. A 3.15-μm-thick film yielded an x-ray full width at half maximum of 171 arcsec. A Hall mobility of 76 200 cm2/V s at 240 K and a full width at half maximum of 174 arcsec have been measured for a 4.85-μm-thick epilayer. Measured Hall data have shown anomalous behavior. A decrease in Hall mobility with decreasing temperature has been observed and room-temperature Hall mobility has increased with thickness. In order to explain the anomalous Hall data, and the thickness dependence of the measured parameters, the Hall coefficient and Hall mobility have been simulated using a three-layer model including a surface layer, a bulklike layer, and an interface layer with a high density of defects. Theoretical analysis has shown that anomalous behavior can be attributed to donorlike defects caused by the large lattice mismatch and to a surface layer which dominates the transport in the material at low temperatures.

High mechanical reliability of back-ground GaAs LSI chips with low thermal resistance : Masanori Nishiguchi, Atsushi Niki, Noboru Goto, Mitsuaki Fujihira and Hideaki Nishizawa. IEEE Trans. Compon. Hybrids mfg Technol.14(4), 848 (December 1991)

We report the first fabrication of a GaSb n-channel modulation-doped field-effect transistor (MODFET) grown by molecular beam epitaxy. The modulation-doped structure exhibits a room temperature Hall mobility of 3140 cm2 V−1 s−1 and 77 K value of 16000 cm2 V−1 s−1, with corresponding sheet carrier densities of 1.3 × 1012 cm−2 and 1.2 × 1012 cm−2. Devices with 1 μm gate length yield transconductances of 180 mS mm−1 and output of 5 mS mm−1 at 85 K. The device characteristics indicate that electron transport in the channel occurs primarily via the L-valley of GaSb above 85 K. The effective electron saturation velocity is estimated to be 0.9 × 107 cm s−1. Calculations show that a complementary circuit consisting of GaSb n- and p-channel MODFETs can provide at least two times improvement in performance over AlGaAsGaAs complementary circuits.

CBE Growth of InP with Triethylindium and Metalorganic Phosphorous Precursors: Bisphosphinoethane and Tertiarybutyl-Phosphine

ABSTRACTTwo metallorganic phosphorous precursors, bisphosphinoethane (BPE) and tertiarybutyl phosphine (TBP), were studied. For indium phosphide (InP) grown using BPE, the measured room temperature and 77K Hall mobilities were 4,200 and 22,000 cm2/Vs, with carrierdensities 5.7E15 and 4.0E15 cm−3, respectively. For InP grown using TBP, the measured room temperature and 77K Hall mobilities were 4,400 and 26,000 cm2/Vs, with carrier densities 6.4E15 and 5.1E15 cm−3, respectively. An impurity build-up at the substrate interface is responsible for the relatively low mobility in the adjacent epitaxial layers. SIMS analysis showed that S and Si are the primary impurities measured in films grown with BPE and TBP, respectively; impurity concentrations increasedwith cracking temperature. The full width at half maximum (FWHM) of donor bound exciton peaks measured by 2.2K photoluminescence for InP grown by BPE and TBP were 0.84 and 1.28 meV, respectively.

High-Quality InSb Growth on GaAs and Si by Low-Pressure Metalorganic Chemical Vapor Deposition

ABSTRACTWe report the first InSb film growth on Si by low-pressure metalorganic chemical vapor deposition. High-quality layers of InSb have been grown on Si and GaAs substrates. InSb films displayed mirror-like morphology on both substrates. X-ray full width at half maximum of 171 arcsec on GaAs and 361 arcsec on Si for a InSb layer thickness of 3.1 μm were measured. Room-temperature Hall mobilities of 67,000 and 48,000 cm2/V.s with carrier concentration of 1.5×1016 and 2.3×1016 cm−3 have been achieved for InSb films grown on GaAs and Si substrates, respectively. A 4.8 μ-thick InSb film on GaAs exhibited mobility of 76,200 cm2/Vs at 240 K.

Influence of thermal annealing on the electron mobility in modulation doped Si/SiGe heterostructures

We grew n-type modulation doped Si/SiGe multiple quantum well structures with the highest electron mobilities reported so far for this heterosystem. The samples were annealed at temperatures between 750 and 950 °C for 1000 s and subsequently characterized by x-ray rocking analysis, secondary ion mass spectroscopy, and temperature dependent Hall measurements. A moderate decrease in room temperature Hall mobility is observed up to annealing temperatures of 900 °C. Above 900 °C the samples become homogeneously doped and show strong Si/Ge interdiffusion at the heteroboundaries. The annealing effects are discussed in terms of dopant and Ge diffusion, and of metastability of the SiGe layers.

Characterization of Te-doped GaSb grown by molecular beam epitaxy using SnTe

The use of SnTe as a source of donor impurities in the growth of n-type GaSb by molecular beam epitaxy (MBE) is investigated. Hall carrier concentrations between 1.23×1016 and 3.7×1018 cm−3 have been obtained with room-temperature Hall mobility as high as 5114 cm2/V s for a lightly doped GaSb layer with nH = 3.8 × 1016 cm−3. The temperature-dependent Hall concentrations have been analyzed according to the two-band model to obtain information about the effect of the band structure of GaSb on the electrical properties. In addition, the effects of V-III flux ratio on Te incorporation in GaSb are studied. The measured carrier concentrations are found to be insensitive to the antimony-to-gallium beam equivalent pressures (from 1.5 to 9) at a growth temperature of 500 °C. These results may lead to SnTe being one of the donor dopants of choice in the MBE growth of n-type GaSb.

On-wafer Hall-effect measurement system

A novel system capable of making on-wafer Hall-effect measurements of a patterned wafer during the fabrication sequence has been developed. A flat, powerful rare-earth magnet provides the magnetic field required. The wafer need only have van der Pauw patterns available for on-wafer measurement capability. Measurement of room temperature Hall mobility can quickly and easily be obtained, making possible detailed study of carrier concentration and mobility variations during wafer fabrication.

Tellurium doping study of GaSb grown by molecular beam epitaxy using SnTe

The application of SnTe as a tellurium source of donor impurities in the growth of n-type GaSb by molecular beam epitaxy (MBE) is investigated. We obtained Hall carrier concentrations ranging from 1.23×10 16 to 3.7×10 18 cm −3. At a growth temperature of 500°C, the estimated donor concentrations are proportional to the arrival rate of the molecular dopants up to 3×10 18 cm −3. Room-temperature Hall mobilities as high as 5114 cm 2/V⋯s were measured for a GaSb layer with n H =3.8×10 16 cm −3. These results, coupled with the intensitivity of the electron concentration to the Sb 4/Ga flux ratio, at a growth temperature of 500°C, may lead to SnTe being one of the donor dopants of choice in the MBE growth of n-type GaSb.

Excimer-laser-induced crystallization of hydrogenated amorphous silicon

The electronic transport properties and structural morphology of fast-pulse excimer-laser- crystallized hydrogenated amorphous silicon (a-Si:H) thin films have been measured. The room-temperature dark dc conductivities and Hall mobilities increase by several orders of magnitude at well-defined laser energy density thresholds which decrease as the impurity concentration in the films increases. The structural morphology of the films suggests an impurity-induced reduction of the a-Si:H melt temperature as the origin of this behavior.