Dependence of Hooge parameter of InAs heterostructure on temperature

The InAs quantum well heterostructure was successfully grown on a semi-insulating GaAs substrate by MBE. On the GaAs substrate, the semi-insulating AlGaAsSb was grown to a thickness of 600 nm as the buffer layer, followed by a 15 nm InAs channel layer and a 35 nm AlGaAsSb doped layer together with 10 nm GaAsSb cap layer successively. The electron mobility and the sheet carrier concentration of the 15 nm InAs heterostructure was about 1 m² V⁻¹ s⁻¹ and 4.5×10¹² cm⁻², respectively, at room temperature. This heterostructure is equivalent to the heavily doped InAs substrate with little change of the electron mobility on temperature. This device has typical 1/f noise characteristics without any large bulge throughout the frequency and the temperature ranges observed. The Hooge parameter was α_H=1×10⁻³ at room temperature, decreasing monotonically with the decreasing temperature down to 5×10⁻⁴ at 50 K, indicating characteristics of the virtually constant mobility and constant carrier concentration device.     

Very wide current-regime operation of an InP/InGaAs tunneling emitter bipolar transistor (TEBT)

A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device can be operated under extremely wide collector current regime larger than 11 decades in magnitude (10⁻¹² to 10⁻¹ A). A current gain of 3.8 is obtained even operated at an ultra-low collector current of 3 × 10⁻¹² A (1.2 × 10⁻⁷ A/cm²). Furthermore, at lower V_BE bias regime (V_BE < 0.4 V), the low base current ideality factors are found. These results reveal that the tunneling probability for holes is very small. Therefore, the emitter injection efficiency is substantially improved.     

Transport and noise properties of CdTe(Cl) crystals

Experimental studies of transport and noise characteristics of CdTe (Cl doped) crystals, prepared by travelling heater method, have been carried out. The basic material is of p-type with p=1.8×10¹⁴ m⁻³, μ_h=0.0065 m² V⁻¹ s⁻¹, μ_e=0.13 m² V⁻¹ s⁻¹. The current and noise spectral density was measured as a function of the sample illumination, voltages across the sample and incident light wavelengths. Two types of effective charge carrier mobility are assumed: namely, the effective transport mobility, which is 0.065 m² V⁻¹ s⁻¹ and the effective noise mobility, which reaches a value of 0.125 m² V⁻¹ s⁻¹, both for high illumination. Under the same conditions, the density of light generated charge carrier pairs is 1.7×10¹⁵ m⁻³. Experimental results are in a good agreement with the four-level recombination model. The values of 1/f noise parameter α range from 4×10⁻⁴ to 2.5×10⁻³. The α parameter grows with almost the photocurrent square root. The signal-to-noise ratio improves if the electric field strength in the CdTe detector is set to a higher value.     

Galvanic corrosion effects in InP-based laser ridge structures

Galvanic corrosion effects in metallized III-V laser structures have been studied. Small gaps present in the metallization can leave exposed semiconductor regions, which are susceptible to localized corrosion in the presence of an electrolyte. Electochemical measurements in two different electrolytes, i.e., 1% HF and concentrated H₃PO₄, were made of test structures comprised of n-type InP, p-type InP, and p-type InGaAs, as well as Au. Polarization measurements were made in all cases relative to a Ag/AgCl reference electrode. Corrosion potentials, measured relative to Au, of 540, 180, and 330 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in 1% HF. Values of 415, 47, and 138 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in concentrated H₃PO₄. Galvanic current densities of 2.0 × 10⁻⁶A/cm², 1.0 × 10⁻⁷ A/cm², and 4.0 × 10⁻⁶ A/cm² were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in 1%HF. Values of 1.2 × 10⁻⁶ A/cm², 1.2 × 10⁻⁷ A/cm², and 1.0 × 10⁻⁶ A/cm² were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in concentrated H₃PO₄. Complementary microstructural studies, using scanning electron microscopy, were done on actual metallized ridge laser structures, consisting of a p-type InP ridge with a p-type InGaAs capping layer and a Ti/Pt/Au metallization. Localized pitting of the InGaAs layer was observed for samples with gaps in the metallization.     

Electron mobility and drift velocity in selectively doped InAlAs/InGaAs/InAlAs heterostructures

An increase in the electron mobility and drift velocity in high electric fields in quantum wells of selectively doped InAlAs/InGaAs/InAsAs heterostructures is obtained experimentally via controlling the composition of semiconductors forming the interface. The electron mobility at the interface in the In_0.8Ga_0.2As/In_0.7Al_0.3As metamorphic structure with a high molar fraction of In (0.7–0.8) is as high as 12.3 × 10³ cm² V⁻¹ s⁻¹ at room temperature. An increase in the electron mobility by a factor of 1.1–1.4 is attained upon the introduction of thin (1–3 nm) InAs layers into a quantum well of selectively doped In_0.53Ga_0.47As/In_0.52Al_0.48As heterostructures. A maximal drift velocity attains 2.5 × 10⁷ cm/s in electric fields of 2–5 kV/cm. The threshold field F _th for the intervalley Γ-L electron transfer (the Gunn effect) in the InGaAs quantum well is higher than in the bulk material by a factor of 2.5–3. The effect of two- to threefold decrease in the threshold field F _th in the InGaAs quantum well is established upon increasing the molar fraction of In in the InAlAs barrier, as well as upon the introduction of thin InAs inserts into the InGaAs quantum well.     

Monolithically integrated long wavelength optical receiver OEICs using InAlAs/InGaAs heterojunction MESFETs (HFETs)

Monolithic optical receiver OEICs have been successfully fabricated on 2" diameter InP substrates by integrating an InGaAs pin photodetector with a simple InAlAs/InGaAs heterojunction MESFET (HFET) structure. Transimpedance receivers based on 1.5 mu m gate length FETs exhibited 3.5 GHz bandwidth and 19.9 pA/ square root (Hz) averaged noise current. Circuit functional yield as high as 67% has been achieved.<>     

Effect of structural parameters on InGaAs/InAlAs 2DEG transport characteristics

The effect of structural parameters on the transport characteristics from 15 to 300 K of molecular beam epitaxy-grown InGaAs/InAlAs two dimensional electron gas structures lattice-matched to InP is determined. The InAlAs buffer layer thickness was varied from 1000 to 10,000Å. One sample also incorporated a InGaAs/InAlAs superlattice. The buffer layer thickness and structure had almost no effect on the mobility or sheet density. The InAlAs spacer layer was varied from 25 to 200Å. Increases in the InAlAs spacer thickness resulted in a monotonically decreasing sheet density and a peak in the mobility versus spacer thickness at 100Å. The highest 77 K mobility was 66,700 cm²/V/sds withN _D =1.2×10¹² cm^?2. The effect of illumination and temperature on the sheet concentration in these structures as well as on “bulk” InAlAs:Si was much smaller than in Al _x Ga_1?x As/GaAs structures or “bulk” Al _x Ga_1?x As, forx?0.30, indicating that devices based on this material system will not be characterized by many of the device instabilities observed in the AlGaAs/GaAs system.     

Electrical properties of InAlAs/InAsxP1-x/InP composite-channel modulation-doped structures grown by solid source molecular beam epitaxy

We report on the electrical characteristics of the two-dimensional electron gas (2DEG) formed in an InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel modulation-doped (MD) structure grown by solid source (arsenic and phosphorus) molecular beam epitaxy (SSMBE). The As composition, x, of strained InAs_xP_1-x was determined by x-ray diffraction analysis of InP/InAs_xP_1-x/InP multi-quantum wells (MQWs) with compositions of x=0.14 to x=0.72. As the As composition increases, the room temperature sheet resistance of InAlAs/InAs_xP_1-x/InP composite-channel MD structures grown over a range of As compositions decreased from 510 to 250 Ω/cm², resulting from the greater 2DEG confinement and lower electron effective mass in the InAs_xP_1-x channel as x increases. The influence of growth conditions and epitaxial layer designs on the 2DEG mobility and concentration were investigated using 300 K and 77 K Hall measurements. As the exposure time of the As₄ flux on the growth front of InAs_xP_1-x increased during growth interruptions, the 2DEG mobility, in particular the 77K mobility, was considerably degraded due to increased roughness at the InAlAs/InAs_xP_1-x interface. For the InAlAs/InAs_0.6P_0.4/InP composite-channel MD structure with a spacer thickness of 8 nm, the room temperature 2DEG mobility and density were 7200 cm²/Vs and 2.5 × 10¹² cm⁻², respectively. These results show the great potential of the InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel MD heterostructure for high frequency, power device applications.     

Low frequency noise sources in InAlAs/InGaAs MODFETs

Detailed analysis of the 1/f low-frequency noise (LFN) in In/sub 0.52/Al/sub 0.48/As/InGaAs MODFET structures is performed, for low drain bias (below pinch-off voltage), in order to identify the physical origin and the location of the noise sources responsible for drain current fluctuations in the frequency range 0.1 Hz-10/sup 5/ Hz. Experimental data were analyzed with the support of a general modeling of the 1/f LFN induced by traps distributed within the different layers and interfaces which constitute the heterostructures. Comparative noise measurements are performed on a variety of structures with different barrier (InAIAs, InP) and different channel (InGaAs lattice matched to InP, strained InGaAs, InP) materials. It is concluded that the dominant low frequency noise sources of InAlAs/InGaAs MODFET transistors in the ON state are generated by deep traps distributed within the "bulk" InAlAs barrier and buffer layers. For reverse gate bias, the gate current appears to be the dominant contribution to the channel LFN, whereas both the gate current and the drain and source ohmic contacts are the dominant sources of noise when the device is biased strongly in the ON state. Heterojunction FET's on InP substrate with InP barrier and buffer layers show significantly lower LFN and appear to be more suitable for applications such as nonlinear circuits that have noise upconversion.     

Admittance spectroscopy of ring diode InGaAs/InAlAs/InP quantum-well structures

The admittance of ring planar diode Au/InGaAs/InP and Au/InGaAs/InAlAs heteronanostructures on i-InP has been studied. The structures are constituted by a silicon ??-doped layer and an InGaAs quantum well (QW) in InP or InAlAs epitaxial layers. An analysis of the capacitance-voltage and conductance-voltage characteristics yielded distribution profiles of the electron concentration and mobility in the vicinity of the QW and ??-doped layer. It is shown that lowering the temperature leads to an increase in the electron concentration and mobility in the QW.     

Study of electrically active defects in n-GaN layer

Deep level defects in both p⁺/n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at E_c−E_t=0.23–0.27 eV with a capture cross-section of the order of 10⁻¹⁹–10⁻¹⁶ cm² for both the p⁺/n and n-type Schottky GaN diodes. For one set of p⁺/n diodes with a structure of Au/Pt/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au and the n-type Schottky diodes, two other common electron traps are found at energy positions, E_c−E_t=0.53–0.56 eV and 0.79–0.82 eV. In addition, an electron trap level with energy position at E_c−E_t=1.07 eV and a capture cross-section of σ_n=1.6×10⁻¹³ cm² are detected for the n-type Schottky diodes. This trap level has not been previously reported in the literature. For the other set of p⁺/n diodes with a structure of Au/Ni/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au, a prominent minority carrier (hole) trap level was also identified with an energy position at E_t−E_v=0.85 eV and a capture cross-section of σ_n=8.1×10⁻¹⁴ cm². The 0.56 eV electron trap level observed in n-type Schottky diode and the 0.23 eV electron trap level detected in the p⁺/n diode with Ni/Au contact are attributed to the extended defects based on the observation of logarithmic capture kinetics.     

Electrical properties of oxidized polycrystalline silicon as a gate insulator for n-type 4H-SiC MOS devices

MOS capacitors were produced on n-type 4H-SiC using oxidized polycrystalline silicon (polyoxide). The polyoxide samples grown by dry oxidation without an anneal had a high interface state density (D_it) of 1.8 × 10¹² cm⁻² eV⁻¹ and the polyoxide samples grown by wet oxidation had a lower D_it of 1.2 × 10¹² cm⁻² eV⁻¹ (both at 0.5 eV below the conduction band). After 1 h Ar annealing, the D_it of wet polyoxide was reduced significantly to 2.6 × 10¹¹ cm⁻² eV⁻¹ (at 0.5 eV below the conduction band). Dry polyoxide exhibits higher breakdown electric fields than wet polyoxide. The interface quality and breakdown characteristics of polyoxide are comparable to published results of low-temperature CVD deposited oxides.     

Luminescence and microstructure of Er/O co-doped Si structures grown by MBE using Er and SiO evaporation

Er and O co-doped Si structures have been prepared using molecular-beam epitaxy (MBE) with fluxes of Er and O obtained from Er and silicon monoxide (SiO) evaporation in high-temperature cells. The incorporation of Er and O has been studied for concentrations of up to 2×10²⁰ and 1×10²¹ cm⁻³, respectively. Surface segregation of Er can take place, but with O co-doping the segregation is suppressed and Er-doped layers without any indication of surface segregation can be prepared. Si_1−xGe_x and Si_1−yC_y layers doped with Er/O during growth at different substrate temperatures show more defects than corresponding Si layers. Strong emission at 1.54 μm associated with the intra-4f transition of Er³⁺ ions is observed in electroluminescence (EL) at room temperature in reverse-biased p–i–n-junctions. To optimize the EL intensity we have varied the Er/O ratio and the temperature during growth of the Er/O-doped layer. Using an Er-concentration of around 1×10²⁰ cm⁻³ we find that Er/O ratios of 1 : 2 or 1 : 4 give higher intensity than 1 : 1 while the stability with respect to breakdown is reduced for the highest used O concentrations. For increasing growth temperatures in the range 400–575°C there is an increase in the EL intensity. A positive effect of post-annealing on the photoluminescence intensity has also been observed.     

Electron mobility and effective mass in composite InGaAs quantum wells with InAs and GaAs nanoinserts

The paper is concerned with the theoretical and experimental studies of the band structure and electrical properties of InAlAs/InGaAs/InAlAs/InP heterostructures containing a composite InGaAs quantum well with InAs and GaAs nanoinserts. From the Shubnikov-de Haas effect, the effective cyclotron mass m _c ^* is determined experimentally and calculated with consideration for the nonparabolicity of the electron energy spectrum. An approach to estimation of the effective mass is proposed and tested. The approach is based on weighted averaging of the m _c ^* of the composite quantum well’s constituent materials. A first proposed heterostructure containing two InAs inserts symmetrically arranged in the quantum well makes a 26% reduction in m _c ^* compared to m _c ^* in the lattice-matched In_0.53Ga_0.47As quantum well possible.     

The detection limit of curved InGaAs/AlGaAs/GaAs hall bars

The work is devoted to the study of noise characteristics of curved Hall bars based on InGaAs/AlGaAs/GaAs semiconductor heterostructures. The noise spectral density S_N(f) was investigated experimentally and the magnetic field detection limit B_N of a flat and similar Hall bar rolled in a tube was defined. The low-frequency spectra of 1/f noise were studied and the dimensionless Hooge noise parameter α_H was determined. The ability to use the curved Hall bars in the devices for measuring weak magnetic fields (<1 μT) was predicted.     

Modelling and simulation of low-frequency broadband LNA using InGaAs/InAlAs structures: A new approach

The ultra-low leakage properties of a novel InGaAs/InAlAs/InP structure have been used to fabricate large gate periphery pHEMTs (up to 1200 μm²) required for wide band low-noise amplifiers (LNA). The devices were characterized and both linear and non-linear models were extracted. LNAs were then designed and compared favourably with the best results reported to date between 0.3 and 2 GHz, still using a 1 μm gate length optical lithography.     

Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction

We have optimized the base electrode for InGaAs/InP based double heterojunction bipolar transistors with a buried emitter-base junction. For the buried emitter-base structure, the base metal is diffused through a thin graded quaternary region, which is doped lightly n-type, to make ohmic contact to the p⁺InGaAs base region. The metal diffusion depth must be controlled, or contact will also be made to the collector region. Several metal schemes were evaluated. An alloy of Pd/Pt/Au was the best choice for the base metal, since it had the lowest contact resistance and a sufficient diffusion depth after annealing. The Pd diffusion depth was easily controlled by limiting the thickness to 50?, and using ample Pt, at least 350?, as a barrier metal to the top layer of Au. Devices with a 500? base region show no degradation in dc characteristics after operation at an emitter current density of 90 kA/cm² and a collector bias, V_CE, of 2V at room temperature for over 500 h. Typical common emitter current gain was 120. An f_t of 95 GHz and f_max, of 131 GHz were achieved for 2×4 μm² emitter size devices.     

Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

A consistent set of epitaxial, n-type conducting ZnO thin films, nominally undoped, doped with Ga or Al, or alloyed with Mg or Cd, was grown by pulsed laser deposition (PLD) on single-crystalline c-plane sapphire (0 0 0 1) substrates, and characterized by Hall measurement, and UV/VIS optical transmission spectroscopy.The optical band gap of undoped ZnO films at nearly 3.28 eV was shifted by alloying with Mg up to 4.5 eV and by alloying with Cd down to 3.18 eV, dependent on the alloy composition. In addition, highly doped ZnO:Al films show a blue-shifted optical absorption edge due to filling of electronic states in the conduction band.The Hall transport data of the PLD (Mg,Zn,Cd)O:(Ga,Al) thin films span a carrier concentration range of six orders of magnitude from 3 × 10¹⁴ to 3 × 10²⁰ cm⁻³, which corresponds to a resistivity from 5 × 10⁻⁴ to 3 × 10³ Ω cm. Structurally optimized, nominally undoped ZnO films grown with ZnO nucleation and top layer reached an electron mobility of 155 cm²/V s (300 K), which is among the largest values reported for heteroepitaxial ZnO thin films so far.Finally, we succeeded in combining the low resistivity of ZnO:Ga and the band gap shift of MgZnO in MgZnO:Ga thin films. This results demonstrate the unique tunability of the optical and electrical properties of the ZnO-based wide-band gap material for future electronic devices.     

Zinc diffusion in InAsP/InGaAs heterostructures

A systematic study of the sealed ampoule diffusion of zinc into epitaxially grown InP, In_0.53Ga_0.47As, In_0.70Ga_0.30As, In_0.82Ga_0.18As, and through the InAsP/InGaAs interface is presented. Diffusion depths were measured using cleave-and-stain techniques, electrochemical profiling, and secondary ion mass spectroscopy. The diffusion coefficients, , were derived. For InP, D₀=4.82 × 10⁻²cm²/sec and E_a=1.63 eV and for In_0.53Ga_0.47As, D₀=2.02 × 10⁴cm²/sec and E_a=2.63 eV. Diffusion into the heteroepitaxial structures used in the fabrication of planar PIN photodiodes is dominated by the effects of the InP/InGaAs interface.     

Optimization of electric properties of high-k zirconium dioxide by varying deposition and annealing conditions

ZrO₂ thin films with a smooth surface were synthesized on silicon by atomic vapor deposition™ using Zr[OC(CH₃)₃]₄ as precursor. The maximum growth rate (7 nm min⁻¹) and strongest crystalline phase were obtained at 400 °C. The increase of the deposition temperature reduced the deposition rate to 0.5 nm min⁻¹ and changed the crystalline ZrO₂ phase from cubic/tetragonal to monoclinic. These films showed no enhancement of the dominating monoclinic phase by annealing. The values of the dielectric constant (up to 32) and leakage current density (down to 1.2×10⁻⁶ A cm⁻² at 1×10⁶ V cm⁻¹) varied depending on the deposition temperature and film thickness. The midgap density of interface states was N_it=5×10¹¹ eV⁻¹ cm⁻². The leakage current and the density of interface states were lowered by the annealing to 10⁻⁷ A cm⁻² at 1×10⁶ V cm⁻¹ and to 10¹⁰ eV⁻¹ cm⁻², respectively. However, this also led to a decrease of the dielectric constant.