摘要:

Ag and Cu interfaces with chemically prepared CdS surfaces have been studied under hydrostatic pressures to 10 kbar. These interfaces exhibit a photovoltaic spectrum at photon energies less thanEgdue to the existence of new states bound at the interface. We find that the pressure coefficient of the interface‐state subband is sensitive to the preparation of the interface even through the atmospheric pressure photovoltaic spectra of the various interfaces studies are very similar.

ISSN:0021-8979    

DOI:10.1063/1.335427

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A transient capacitance method is presented, which enables the study of electric‐field‐enhanced emission from a continuum of surface states at the Si/SiO2interface. The enhancement of trap emission is measured in Al‐SiO2‐Si structures by the variation in the transient capacitance signal detected under a constant applied electric field, the trap emission having been previously activated by application of a higher electric field (excitation bias). The dipolar relaxation contribution to the transient signal observed in these structures is substracted during the experiment. The decrease in the resulting transient signal with the excitation bias clearly reveals the donor nature of the interface traps studied. Since the surface traps are highly localized at the Si‐SiO2interface, the electric field on the impurity is perfectly known. Assuming the sole presence of the Frenkel‐Poole effect in our experimental conditions, the barrier lowering is obtained as a function of the applied electric field. From these data, the shape of a portion of the impurity potential well is deduced for different levels in the Si gap, in the direction normal to the Si‐SiO2interface. The results are in good agreement with a coulombic potential barrier at some distance from the impurities (∼10 nm).

ISSN:0021-8979    

DOI:10.1063/1.335218

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The generation of a bulk positive charge in SiO2layers of silicon gate metal‐oxide‐silicon (MOS) devices, under the conditions of high‐field and charge injection is studied. The time dependence of the positive charge and its spatial distribution as a function of the oxide thickness and electric field are all consistent with an impact ionization‐recombination model which takes into account both the spatial and the field dependence of the ionization probability. The nature of the ionization, either band‐to‐band, or traps ionization, is still unknown. Bulk positive charge of the same nature is also formed in Al gate oxides. Nevertheless, it was not always observed in previous works since a much larger Si‐SiO2interfacial positive charge is also generated in these samples.

ISSN:0021-8979    

DOI:10.1063/1.335219

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A theory of the ac surface photovoltage is presented for the case of surface recombination of carriers via mobile centers located in the insulator in the region adjacent to the interface. The surface photovoltage relaxation time for this recombination mechanism is shown to be strongly dependent on the modulation frequency of the incident light, while the relaxation time is frequency independent if the recombination of carriers occurs via conventional, spatially fixed, surface states. The dependence of the ac surface photovoltage on the modulation frequency of the incident light was measured forn‐Si/native oxide andn‐GaAs/native oxide systems. The strong frequency dependence of the surface photovoltage relaxation time observed for ann‐Si/native oxide system under depletion conditions indicated that the carrier recombination at this interface occurs mainly via mobile oxide centers. The relaxation time inn‐GaAs/ native oxide system was found to be frequency independent, confirming previous conclusions that surface states in GaAs are associated with defects located on the semiconductor side of the interface.

ISSN:0021-8979    

DOI:10.1063/1.335220

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have combined current‐voltage (I‐V) and capacitance‐voltage (C‐V) measurements onn− GaAs–Al0.4Ga0.6As–n+ GaAs capacitors with different thicknesses of Al0.4Ga0.6As to determine the conduction‐band discontinuity at the Al0.4Ga0.6As–n+ GaAs interface. Undoped AlxGa1−xAs deposited by molecular‐beam epitaxy contains negative charge. We calculate the effect of band bending in undoped AlxGa1−xAs due to negative charge on measured barrier heights and onC‐Vcurves. The temperature dependence ofI‐Vcurves is analyzed in terms of thermionic emission to derive barrier heights at then+ GaAs–Al0.4Ga0.6As interface &fgr;G. Measured values of &fgr;Gare proportional to the square of the insulator thickness,w, showing that negative charge is uniformly distributed through undoped Al0.4Ga0.6As. Combining values of Fermi energy and band bending at zero bias with &fgr;Gat zero Al0.4Ga0.6As thickness, we find that the value of the barrier discontinuity forn+ GaAs–Al0.4Ga0.6As is ∼0.30 V. This corresponds to a ratio of conduction‐band discontinuity &Dgr;ECto band‐gap difference &Dgr;EGof 0.63±0.03, which is appreciably less than the value 0.85±0.03 that is widely accepted. We find that the dielectric constant of Al0.4Ga0.6As is more temperature dependent than that of GaAs between 77 and 250 K.

ISSN:0021-8979    

DOI:10.1063/1.335221

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Fowler–Nordheim tunneling electron injection is performed at 295 and 77 K in metal‐oxide‐semiconductor capacitors. In both cases the positive charge generated at the Si‐SiO2interface is found to be the ‘‘anomalous’’ positive charge related to the slow states. At low temperature this charge is created at a faster rate than at 295 K for both positive and negative polarity. Its saturated density, on the contrary, strongly depends on the polarity of the applied bias voltage at low temperature, being much smaller during injection at positive bias. Fast and slow states appear only after the sample is heated to room temperature. While interband impact ionization is ruled out as a possible generation mechanism, the results are consistent with the idea that the hot injected electrons lose their energy at the anode‐SiO2interface by emitting an unidentified species which is responsible for the generation of the interfacial damage. A field‐ and temperature‐activated migration of the positive defects from the sites of formation to the interface must occur before slow and fast states are observed. The correlation between slow states and hole traps is discussed.

ISSN:0021-8979    

DOI:10.1063/1.335222

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Avalanche and Fowler–Nordheim tunneling electron injections have been performed at constant current on a broad variety of differently processed Al‐gate metal‐oxide‐semiconductor capacitors. It is found that the same type of positive charge (the ‘‘slow states’’) is generated during low‐field and high‐field electron injection. The maximum amount of positive charge which can be generated at a given electric field depends on processing and increases linearly with the average field in the oxide. However, the rate at which the positive charge is generated is controlled uniquely by theanodefield, for a given polarity of the gate voltage. It follows that the role of the electron traps in the bulk SiO2—independentoftheirnature—is that of increasing both the rate and the total number of created defects by enhancing, respectively, theanodefield, as a result of the distortion of the potential in SiO2, and theaveragefieldwhich must be increased to maintain a constant injected current. Processes described earlier for the generation of the interfacial defects such as interband impact‐ionization and water‐triggered mechanisms, do not account for the experimental results. In particular, the role of the water‐related electron traps appears to be simply ‘‘electrostatic’’—as for other electron traps, such as arsenic—rather than ‘‘electrochemical,’’ as previously proposed. Instead, it is suggested that during the hot electron injection, a positive or neutral species emitted from theanodicregion propagates to the Si‐SiO2interface creating the damage.

ISSN:0021-8979    

DOI:10.1063/1.335223

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Electrical measurements were made onn+GaAs‐(Al,Ga)As‐n−GaAs andp+GaAs‐(Al,Ga)As‐p−GaAs capacitors. Current conduction is due to thermionic emission at low bias voltages and high temperatures. At low temperatures and high fields Fowler‐Nordheim tunneling contributes to the conduction process. An invertedn‐type capacitor analogous to an inverted modulation doped structure shows electrical characteristics comparable to the ‘‘normal’’ structure grown under optimized conditions. Conduction‐ and valence‐band discontinuities were calculated from measurements of thermionic emission barrier heights as a function of Al mole fraction in the (Al,Ga)As. A conduction‐band discontinuity of 65% of the total band‐gap discontinuity between GaAs and (Al,Ga)As, independent of Al mole fraction, was deduced. A classical theory for the capacitance voltage characteristics ofp+GaAs‐(Al,Ga)As‐p−GaAs structures is presented.

ISSN:0021-8979    

DOI:10.1063/1.335224

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A method is presented for determining the minority‐carrier diffusion length and surface recombination velocity in passivated, shallow junction semiconductor devices. The method is particularly useful with devices where the minority‐carrier diffusion length is comparable to the diameter of the electron beam interaction volume. A gaussian beam profile is convoluted with a theoretical model for electron‐beam‐induced current and the results used to determine the minority‐carrier diffusion length from measured data. The surface recombination velocity is estimated from the dependence of the measured minority‐carrier diffusion length on the electron beam accelerating voltage. The technique is applied to a photovoltaic infrared sensor device made in mercury‐cadmium‐telluride.

ISSN:0021-8979    

DOI:10.1063/1.335225

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We discuss a new technique for measuring the net carrier concentrations, layer thicknesses, and deep level spectra of epitaxial InP and related compounds used in photonic device applications. The technique involves the formation of an organic‐on‐inorganic (OI) semiconductor contact barrier by vacuum sublimation of the compound: 3, 4, 9, 10‐perylenetetracarboxylic dianhydride onto an inorganic semiconductor wafer. The OI barriers are reproducible from wafer to wafer, and can be as high as &fgr;Bn≊0.55 V over the entire range of InGaAs (P) compounds lattice matched to InP. High voltages (≳100 V in some cases) can be applied to the small area OI devices (as defined by an ohmic contact pad deposited on the organic film), allowing for deep depletion. Thus, high resolution carrier concentration measurements over extensive distances in all three wafer dimensions are obtained. These data are used to derive both the doping levels and layer thickness contours over the crystal surface. Finally, the OI devices can be removed after wafer evaluation, and the wafer can then undergo processing into conventional devices with no apparent degradation of performance when compared with control wafers that have not undergone OI diode evaluation.

ISSN:0021-8979    

DOI:10.1063/1.335226

出版商:AIP    

年代:1985

数据来源: AIP