摘要:

We report absorption measurements on two types of long-wave infrared detector structures. Both types were grown by ultrahigh vacuum chemical vapor deposition, and were characterized by multiple analytic techniques. In both multiple quantum well (MQW) and heterojunction internal photoemission (HIP) structures, it is found that free-carrier absorption is dominant for normally incident radiation. The measured absorption is fit well by the classical expression for free-carrier absorption, with scattering times of about10−14 s(MQW) and5×10−15 s(HIP). The measured absorption is used to evaluate the responsivity that results when all carriers energetically able to surmount the barrier are collected. Based on this analysis, higher responsivity is predicted for HIP detectors, largely because of the greater density of initial states. The responsivity obtained in practice depends upon the photoconductive gain (MQW detectors) or the escape probability (HIP detectors). The escape probability for HIP detectors is measured in Part II. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366324

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

GexSi1−x/Siheterojunction internal photoemission (HIP) detectors with thresholds in the medium-wave infrared and long-wave infrared (LWIR) regions were fabricated and characterized. Measurements of the photoresponse are fit well by a theory which takes into account the scattering of excited carriers. The probability of escape of an excited hole is calculated and compared with that observed in another detector, the multiple quantum well structure. It is shown that HIP detectors can achieve background-limited performance in the LWIR region when operated at 40 K.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366325

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We studied capacitance and parallel resistance in resonant tunneling diodes as a function of the doping density in the emitter and the collector regions. Capacitance was obtained by analyzing resonance in the admittance measured. Our data show that the capacitance varies with the doping density, and that the capacitance is smaller than the value expected from the growth parameters. Electron density modulation exists around the barriers, and capacitance has doping density dependence as a result of the modulation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366384

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study of severalSi0.8Ge0.2p-channel heterostructures with self-aligned poly-Si metal–oxide–semiconductor gates were carried out. A novel fabrication process was developed which is compatible with the strained Si/SiGe system, and it has allowed Hall and resistivity measurements to be performed at room temperature and at 4.2 K. The structures were numerically modelled to calculate the charge distribution with temperature and with gate voltage and the results have shown good agreement with experiment. Hall measurements at 4.2 K have shown consistent SiGe channel Hall mobility enhancements of×3over theSiO2/Sichannels in the same devices. Room temperature effective mobilities were measured for a buriedSi0.8Ge0.2p-channel metal–oxide–semiconductor field-effect transistor heterostructure using capacitance–voltage measurements to calculate the carrier density. Mobilities are consistently over300 cm2/V sand the low temperature studies, together with measurements of comparable modulation doped heterostructures, and secondary-ion-mass spectroscopy depth profiles suggest that this mobility is at present limited by the quality and proximity of theSiO2/Siinterface. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366385

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new formalism is reported for the analysis of the current–voltage(I–V)characteristics of a tunnel metal-insulator-semiconductor (MIS) device, which considers a bias dependent distribution of interface states and barrier lowering due to the image force. Our theoretical expression for theI–Vcharacteristics is general in the sense that it is applicable even under conditions when both the thermionic emission and the diffusion mechanisms of current transport compete with each other. The method is ideal for new epitaxial materials and devices where the carrier density is not known precisely beforehand. A self-consistent method of analysis is reported to determine the characteristic parameters of MIS diodes, using simultaneously theI–Vand capacitance–voltage data as a function of temperature. This computational analysis has been used to examine the current transport mechanism in anAu/p-InPepitaxial MIS diode. The experimental verification of the theory and computational analysis is done by comparing the values of the interface state density distribution in thermal equilibrium with the semiconductorNss,obtained from the forwardI–Vcharacteristics, with those directly measured by the multifrequency admittance method. Excellent agreement from these comparisons strongly supports the validity of the theory. Over the temperature range of 200–393 K, our results indicate that the interfacial layer-thermionic emission was clearly the dominant mechanism of the forward current transport in an MIS fabricated on a lightly doped InP:Zn epitaxial layer. The transmission coefficient through the insulator layer obtained from the reverseI–Vcharacteristics was&thgr;p=1.43×10−3±7&percent;from which we estimate an oxide thickness of 2.2 nm. The analysis of the barrier height&fgr;b0versus temperature, obtained from 1 MHzC–Vdata provided a value&fgr;0=1.06 V±10&percent; for the zero bias and zero temperature barrier height. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366386

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By calculating the current–voltage relation for a quantum-size GaAs/AlGaAs heterojunction field effect transistor, we have shown that the electronic near-ballistic transport from the source to the drain is ideal only at zero source-drain bias in the absence of scattering centers. The electron transmission coefficient of the near-ballistic transport reduces following the increase of the source-drain bias so that the source-drain current is lower than the one at ideal transmission condition. The current is further reduced when impurities are introduced and the current reduction depends on the concentration and spatial configuration of impurities. Together with our early work we have shown that the ionized impurities and heterointerface roughness are two important factors in determining the ballistic transport properties in a heterojunction field effect transistor. An optimal current is reached when the AlGaAs spacer in a usual GaAs/AlGaAs heterojunction transistor is about 100 Å thick. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366387

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article we show the effect on the dc and rf transport characteristics of dipole doping at the collector heterojunction in an InP/InGaAs double heterojunction bipolar transistor. We show how the switching characteristics of devices with abrupt undoped InGaAs/InP collector heterojunctions can almost be eliminated by using the dipole doping at that interface and how the high-frequency performance is also improved. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366388

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have experimentally studied the electron velocity overshoot and the mechanism of its degradation in the inversion layer of sub-0.1 &mgr;m metal–oxide–silicon (MOS) field-effect transistors. Both silicon-on-insulator (SOI) and bulk structures were studied. At low transverse electric fields, that is, for low carrier densities in SOI devices under low gate drive conditions, it is possible to achieve electron velocity overshoot due to nonstationary transport in the sub-0.1 &mgr;m region. However, it is very difficult in MOS structures to improve electron velocity at high surface electron densities because of the reduced electron mobility in high transverse fields. Moreover, the surface electron density of MOS structures is reduced when a low channel impurity concentration is chosen to improve low field mobility; this results from the expanded inversion layer width. These results indicate the physical limitations of scaled MOS structures with regards to the realization of higher current capabilities. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366389

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The kinetics of the aging of atomic layer epitaxy ac thin-film electroluminescent devices was studied. In a first series of experiments, we aged devices at different temperatures from 50 to 190 °C, and measured the steady-state transferred charge versus voltage characteristics. From monitoringQ145 V,the charge transferred at 145 V, we could trace the relationship betweenQ145 Vand the aging time. The aging process was found to be temperature dependent, and we could deduce an activation energy of 0.34 eV. In a second series of experiments, devices were aged 16 h at room temperature and subsequently heat treated at different temperatures from 250 to 450 °C. Monitoring againQ145 V,we found that the devices recover from aging following the relationship−krecot=ln[Q145 V/Q145 V(t=0)],wheretis the heat treatment time. The recovery rate constantkrecowas found to have an activation energy of 1.3 eV. In a last series of experiments we found the aging rate to be proportional with the transferred charge. Possibly aging is a process of defect creation at the interface near the substrate. For this creation thermal energy and the energy of the accelerated electrons are needed. The defects can be annihilated by heating the device above 350 °C. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366390

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Responding to the increasing demand for miniaturization and circuit integration of rf inductors we analyze various aspects of designing planar inductive circuits based on magnetic films as well as demonstrate substantially enhanced inductance characteristics for some prototype structures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366391

出版商:AIP    

年代:1997

数据来源: AIP