Free Carrier Profiles Research Articles

Sputtered TiW/Au Schottky barriers on GaAs

High quality stable Schottky barriers are required for GaAs diodes and MESFETS used in mixers and analog and digital ICs. The TiW/Au system has been shown to be quite stable on GaAs. TiW/Au Schottky barriers were deposited on bulk GaAs by rf diode and rf magnetron sputtering. In addition, Ti/W/Au Schottky barriers were deposited by rf magnetron sputtering and e‐beam deposition. Capacitance–voltage and current–voltage measurements, along with Auger analysis were done to determine diode quality. A marked improvement in barrier height and reverse bias characteristics (I–V) was obtained by utilizing magnetron sputtering and reducing deposition power. Free carrier profiles showed evidence of some damage, even at extremely low power levels.

Modeling the influence of carrier profiles on MESFET characteristics

Continuing development of materials methods and the need to improve MESFET device performance calls for accurate modeling of the effect of free-carrier profiles upon MESFET performance. A computer program known as SATVO is described which provides, by means of a numerical solution, saturation characteristics and gate-electrode capacitances for devices of specified geometry fabricated from layers of any profile which may be specified by either Gaussian expressions (as for ion-implanted layers) or by piecewise-linear descriptions. Examples of the use of this program are also provided.

Complex free-carrier profile synthesis by ’’atomic-plane’’ doping of MBE GaAs

Doping solely during periods when growth was suspended has been used to synthesize profiles not easily achieved by conventional doping techniques. Suspension of growth under arsenic stabilized conditions allows Ge doping to produce n-type complex profiles with reduced autocompensation. At higher temperatures, autocompensation becomes apparent. Under gallium stabilized conditions, heavily autocompensated n-type layers resulted, consistent with a nonunity incorporation coefficient.

Laser-irradiation effects on unencapsulated GaAs studied by capacitance spectroscopy

The effect of Q-switched ruby-laser irradiation on unencapsulated unimplanted bulk GaAs has been investigated by means of deep-level transient spectroscopy (DLTS) and C-V carrier profiling. It was found that the concentration of a deep-level center (Ec−0.83 eV) assigned to the A center decreases considerably as a result of laser irradiation, and that no deep levels (electron traps) more than 3×1013/cm3 are induced by the laser irradiation on the uncapped surface at a power level suitable for the recrystallization of an amorphous layer produced by ion implantation. No significant change in the free-carrier profile at a depth deeper than 1500 Å from the surface was observed after the laser irradiation.

Fast current pulse m.o.s. deep-depletion technique for profiling thin epitaxial and ion-implanted layers

An m.o.s. technique is described for making free-carrier profile measurements on thin layers using a current pulse of a few microseconds duration. The method minimises distortion of the results due to surface states and enables the profile right up to the semiconductor surface to be determined

Fast current pulse m.o.s. deep-depletion technique for profiling thin epitaxial and ion-implanted layers

An m.o.s. technique is described for making free-carrier profile measurements on thin layers using a current pulse of a few microseconds duration. The method minimises distortion of the results due to surface states and enables the profile right up to the semiconductor surface to be determined

I. Luminescence and Free Carrier Decay Times in Semiconductors Containing Isoelectronic Traps

This paper describes the measurement of free carrier decay profiles over the temperature range 7°–300°K for GaP:N, GaP:Bi, CdS:Te, and ZnTe:O following their excitation by pulses of electrons from a Van de Graaff accelerator. Contactless microwave transmission and reflectivity techniques were employed to measure the transient conductivity changes. The studies were made principally to obtain a more complete understanding of the recombination mechanisms previously proposed to be operative in CdS:Te and ZnTe:O on the basis of luminescence decay time data. The gross features of the temperature dependence of the free carrier lifetimes correlate well with the luminescence decay time data. Differential equations, formulated to describe the temperature-dependent kinetics, were solved by a combination of numerical and analytical methods to obtain the transient luminescence and free carrier decay profiles. The solutions depend very weakly upon certain capture coefficients. The major variable parameter is in both cases the binding energy ε of the majority carrier in the Coulomb field of the charged isoelectronic trap. For CdS:Te, with εh=20 meV, good agreement was obtained between the calculated and observed free carrier and luminescence decay profiles, thereby providing good support for the model of the recombination mechanism. For ZnTe:O with εe=20 meV, agreement is adequate for the luminescence profiles, but only semiquantitative for the free carrier decay profiles. Reasons for the discrepancies are discussed. For all the materials, at the lowest temperatures, the results indicate very rapid and stable trapping of the carriers with no evidence of a post-excitation conductivity. This is in keeping with the occurrence of highly radiative transitions at these temperatures.