Temperature dependence of the electron impact ionization in InGaP-GaAs-InGaP DHBTs

Temperature dependence of electron impact ionization in InGaP-GaAs-InGaP double heterojunction bipolar transistors (DHBTs) were comprehensively studied in the temperature range of 300 to 450 K. It has been found that, as the temperature increases, the electron multiplication in the InGaP collector is found to be weakly reduced, which results in a relatively small negative temperature dependence of junction breakdown. The temperature dependence of electron impact ionization at elevated temperatures for InGaP material is investigated based on the electron multiplications measured from the InGaP collector region. An empirical expression is obtained to predict the electron ionization coefficients at elevated temperature up to 450 K in the electric field range of 380 to 650 kV/cm. As compared to InP and GaP binaries, the ternary InGaP shows a lower electron ionization coefficient and much weaker temperature dependence. We found that, introducing additional scattering mechanism such as alloy scattering would provide a better interpretation on the low electron impact ionization and its weak temperature dependence observed in InGaP.     

The band structure dependence of impact ionization by hot carriers in semiconductors: GaAs

We present the first systematic study of the dependence of impact ionization by electrons and holes upon the details of the electronic band structure. Our measurements, made in GaAs, establish the crucial role of the ionization threshold energy, and its location in the Brillouin zone, in determining the ionization rates. This relationship is apparent in the dependence of impact ionization rates on the temperature of the lattice, compositional changes for the alloy GaAs_1-xSb_x, and the orientation and strength of the electric field. The strong dependence of impact ionization upon specific features of the electronic band structure is a new principle which can be used to study the nature of electronic states in a wide variety of semiconductors through hot-carrier behavior.     

Investigation of impact ionization in thin GaAs diodes

The electron and hole multiplication coefficients, M_e and M_h, respectively, have been measured in thin GaAs homojunction PIN and NIP diodes and from conventional ionization analysis the effective electron and hole ionization coefficients, α and β, respectively, have been determined. The nominal intrinsic region thickness w of these structures ranges from 1.0 μm down to 25 nm. In the thicker structures, bulk-like behavior is observed; however, in the thinner structures, significant differences are found. As the i-regions become thinner and the electric fields increase, the M_e/M_h ratio is seen to approach unity. The experimental results are modeled and interpreted using a semianalytical solution of the Boltzmann equation. In thin (w⩽0.1 μm) devices the dead space effect reduces effective ionization coefficients below their bulk values at low values of carrier multiplication. However, overshoot effects compensate for this at extremely high fields (⩾1×10³ kV/cm)     

Temperature dependence of electron saturation velocity in GaAs

Electron saturation velocity is determined from the space charge resistance R/sub c/ and microwave impedance Z/sub d/ of GaAs IMPATT diodes under linear conditions. Comparison between experimental measurement and theory is used in a large frequency bandwidth (2-18 GHz) at different temperatures (T>     

Temperature dependence of the Gunn threshold in GaAs

Measurement of the temperature dependence of the threshold for transferred electron instabilities in GaAs gives (1/IP(300))×(dIP/dT=?2.4±0.2×10?3 K?1, independent of carrier concentration The threshold field decreases with decreasing T and depends on carrier concentration. Reasonable agreement is obtained with Monte Carlo calculations based on ?-L-X ordering.     

Temperature dependence of impact ionisation rates in GaAs between 20° and 200°C

We report the temperature dependence, between 20° and 200°C, of free carrier impact ionisation rates in GaAs along the <100>, <110> and <111> directions for the electric field range 4-5 × 105 V/cm. These results should be of interest for the design of avalanche devices such as Impatt diodes which have high operating temperatures.     

Inclusion of impact ionization in the backgating of GaAs FETs

It is shown that the familiar threshold behavior of the backgate current of GaAs MESFETs has hysteresis. This is associated with an S-type negative differential conductivity (S-NDC) of the semi-insulating substrate. It is difficult to account for this hysteresis using conventional trap-fill-limited (TFL) theory, and it is attributed to the impact ionization of traps in the substrate. A simple model of this ionization, involving two trap levels, is used to incorporate its effect into an existing analytical model of GaAs FETs. The result is a qualitative interpretation of the backgating characteristics of GaAs MESFETs. The calculations show that a simple combination of two ohmic elements to represent parasitic resistances, and a nonohmic one to represent impact ionization in the substrate, can imitate the observed backgating behavior     

Temperature dependence of backgating effect in GaAs integrated circuits

The backgating effect in GaAs IC's has been found to be temperature dependent. The threshold voltage for backgating increases with temperature, resulting in lower backgating at higher temperatures. The measured activation energy of the backgating threshold versus temperature is 83 meV, in agreement with the energy difference between the Fermi level and the EL2 level at the surface of semi-insulating GaAs.     

The reduction of backgating in GaAs MESFETs by impact ionization

The reduction of drain current due to reverse substrate bias in GaAs MESFETs fabricated on EL2-compensated substrates is recovered with the application of sufficient drain bias. The recovery is shown to be due to the compensation of the negative space charge at the channel-substrate interface by holes generated by impact ionization in the MESFET channel. Illumination raises the value of drain bias needed for current recovery due to the requirement of additional hole flux to offset the effects of optically generated electrons on EL2 occupancy. Simulation results show that the channel current becomes independent of substrate bias when the bias value is sufficient to completely delete the p-type surface layer     

Temperature dependence of GaAs/AlGaAs multiquantum barrier lasers

A GaAs/AlGaAs laser loaded by a multiquantum barrier (MQB) is reported, and its temperature-threshold characteristic has been systematically examined. It has been found that this characteristic is improved by introducing the MQB, and this improvement is reflected in the barrier height. The actual barrier heights of a MQB-loaded structure under biased conditions are also discussed, considering the Fermi level in the MQB region     

Tensile CESL-induced strain dependence on impact ionization efficiency in nMOSFETs

Process-induced strain dependence of impact ionization efficiency (IIE) in nMOSFETs with a tensile contact etch stop layer (CESL) is presented for the first time. From the universal relationship between the IIE and the electric field in the pinch-off region, a difference in the IIE of nMOSFETs between without and with the tensile CESL is found. This result can be mainly attributed to the narrowing effect of the bandgap energy caused by the tensile CESL-induced strain into the channel, i.e., the reduced threshold energy for impact ionization. In addition, the wafer-bending experiments can further provide strong evidence for the bandgap energy narrowing. It means that the IIE measurement could serve as a reliable monitor of the process-induced strain into the channel.     

Temperature dependence of the high-field velocity of electrons in n GaAs

The drift velocity of electrons at high electric fields has been measured in n GaAs by the time-of-flight technique. The range of electric fields used was 20 to 85 kV/cm and the experiments were performed at temperatures of 158, 300, 340 and 400 K. All the results show the velocity to decrease slowly as the field is increased.     

Temperature dependence of carrier ionization rates and saturated velocities in silicon

The temperature dependencies of the carrier ionization rates and saturated drift velocities in silicon have been extracted from microwave admittance and breakdown voltage data of avalanche diodes. The avalanche voltage and broadband (2–8 GHz) microwave small-signal admittance were measured for junction temperatures in the range 280 to 590 K. An accurate model of the diode was used to calculate the admittance characteristic and voltage for each junction temperature. Subsequently, the values of ionization coefficients and saturated velocities were determined at each temperature by a numerical minimization routine to obtain the best fit between the calculated values and measured data. The resulting ionization rates are well fitted by the temperature dependent model developed by Crowell and Sze from the Baraff ionization-rate theory. The carrier scattering mean free path lengths, average energy loss per collision, and relative ionization cross section are obtained from the best fit agreement between the scattering model and experimental data. The parameter values determined here relevent for use with the above theory are the following:Parameter Holes Electrons ε_r(eV) 0.063 0.063 ε_i(eV) 1.6 1.6 λ_oo(Å) 81.2 77.4 σ 0.391 0.593 The values and temperature dependence of the saturated carrier velocities determined are in good agreement with other published results. At 300 K the low field (E?10⁴ V/cm) saturated velocity for electrons and holes is 10.4 and 7.4×10₆ cm/sec, respectively. The results obtained in this study are of general use for the modeling of effects related to avalanche breakdown and high-field carrier transport in silicon.     

Temperature dependence of threshold current of GaAs quantum well lasers

The radiative recombination rate in a quantum well structure is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs quantum well laser has low temperature sensitivity (T0 ? 330 K for T > 300 K).     

Temperature dependence and persistent conductivity of GaAs MESFETswith superlattice buffers

The DC characteristics of GaAs MESFETs with superlattice buffers were studied at room and liquid-nitrogen temperatures. It was found that the superlattice buffers provide effective screening for the active layers at room temperature and in the dark. At 77 K, however, persistent conductivity induced by ambient light or high gate bias was observed. The origin of the conductivity is presumably due to the activation of deep centers associated with the superlattice     

Negative base current and impact ionization phenomena inAlGaAs/GaAs HBTs

Impact ionization phenomena in the collector region of AlGaAs/GaAs heterojunction bipolar transistors give rise to base current reduction and reversal. These phenomena can be characterized by extracting the M-1 coefficient, which can be evaluated by measuring base current changes. Measurements of M-1 are affected at low current densities by the presence of the collector-base junction reverse current I_CBO. At high current densities, three effects contribute to lower the measured M-1 value: voltage drops due to collector (R_C) and base (R_B) parasitic resistances, device self-heating, and lowering of the base-collector junction electric field due to mobile carriers. By appropriately choosing the emitter current value, parasitic phenomena are avoided and the behavior of M-1 as a function of the collector-base voltage V_CB in AlGaAs/GaAs HBTs is accurately characterized     

Growth and photoreflectance characterization of GaAs impact ionization avalanche transit time diodes

The organometallic vapor phase epitaxial growth of GaAs double-drift Read impact ionization avalanche transit time diodes where the p-type layers were doped with carbon is described. Ka-band oscillation testing yielded average performance of 3.5 W with 16% efficiency for pulse lengths >1 μs and 10.5 W with 13% efficiency for pulse lengths <1 μs; these RF performances are similar to conventionally grown vapor phase epitaxy IMPATTs where the p-type dopant was zinc. Photoreflectance spectra obtained from diode structures were found to be dominated by the electric field in the avalanche region and hence are sensitive to the amount of charge in the doping spikes that determine the electric field in that region.     

Temperature dependence of InAs/GaAs quantum dots solar photovoltaic devices

This paper presents the temperature dependence measurements characterisation of several InAs/GaAs quantum dots （QDs） solar cell devices. The devices with cylindrical geometry were fabricated and characterised on-wafer under 20 suns in a temperature range from 300°K to 430°K. The temperature dependence parameters such as open circuit voltage, short circuit density current, fill factor and efficiency are studied in detail. The increase of temperature produces an enhancement of the short circuit current. However, the open circuit voltage is degraded because the temperature increases the recombination phenomena involved, as well as reducing the effective band gap of the semiconductor.     

Impact ionization in GaAs MESFETs

A method to measure impact ionization current in GaAs MESFETs is presented. The impact ionization current is then used to calculate the maximum electric field in the channel and the impact ionization coefficient. Data for the electron impact ionization coefficient in 〈110〉 GaAs are extended beyond previous studies by five orders of magnitude. Impact ionization is taken into account in a new gate current model