D. J. Moss

Third harmonic generation as a structural diagnostic of ion‐implanted amorphous and crystalline silicon

We demonstrate the use of third harmonic generation as a probe of the bulk symmetry properties of semiconductors. Using 20 ns, 1.06 μm laser pulses we have applied this probe to structural diagnostics of (100) annealed and unannealed Si wafers implanted with boron and arsenic ions at dosages above and below the threshold for amorphization. The presence of free carriers with densities up to 1021 cm−3 is found to increase the intensity but not alter the symmetry characteristics of the third harmonic light; the enhancement in the light level is attributed to a change in the reflectivity.

Dispersion in the anisotropy of optical third-harmonic generation in silicon.

We present what are to our knowledge the first theoretical and experimental results for dispersion in the anisotropy (sigma) of chi?((3)) associated with optical third-harmonic generation in Si. The theory is based on a full empirical tight binding band-structure calculation, and the results agree well with our measurements for 0.72 microm < lambda < 1.9 microm. The calculated low-frequency limit of sigma agrees with measurements from the literature better than earlier calculations do. In addition, the dispersion in the relative phase of chi1212((3))/chi1111((3)) also shows good agreement with experiment.

Subnanosecond time‐resolved photoconductive response of semiconducting diamond

The time‐resolved photoconductive response of several natural and synthetic semiconducting (IIb) diamonds has been measured at room temperature using an optoelectronic cross‐correlation technique. The response times are between 100 and 300 ps, indicating a capture cross section for the photoexcited holes of ∼4×10−13 cm−2. We have found that IIb diamonds can serve as a simple, rugged pulsed laser detector for 0.45

Picosecond Photoconductive Switching In Semiconducting And Insulating Natural Diamond

We have used 20 psec, 1.06 and 0.35 μm pulses to time resolve the photoconductive response of semiconducting and insulating natural diamonds, respectively. Pairs of diamonds were mounted in tandem in a biased coaxial transmission line and the time response of each was obtained by using a sample and gate technique that yields the cross-correlation of the induced photocurrents. Typical response times of 100-500 psec were determined for the semiconducting diamonds at room temperature; these times are explained in terms of capture of photoexcited holes by excited states of the boron acceptors in these p-type materials. The response time of the insulating diamonds was determined by using a semiconducting and insulating diamond in tandem, with the former illuminated by by 1.06 μm light and the latter by 0.35 μm light. In each case photoconductivity is induced via impurity to band transitions. The response time of the insulating diamonds is ≤500 psec. Because of this fast time response, as well as high dielectric strength and thermal conductivity, insulating diamond shows promise as a fast high voltage switch with voltage hold-off capability of (~10 kV.

Analysis of picosecond optoelectronic cross‐correlation switches

We analyze the use of tandem, photoconducting gates in a biased transmission line for picosecond, optoelectronic cross‐correlation measurements. In general the integrated photoinduced current is a function of the time delay between excitation pulses and is the sum of the cross correlation of the induced conductivities and a constant background. We consider two possible circuits, which differ in that one contains an isolation attenuator between the two switches which helps improve the contrast ratio of the cross correlation and dc outputs. We obtain the contrast ratios and the absolute outputs of the two circuits as a function of circuit parameters. We show that gate transmission saturation leads to distortions in the cross‐correlation function and induced asymmetries which reflect the different functions performed by the two switches. Certain elements of the theory are compared with experimental results on the picosecond photoconductive response of semiconducting diamond. We, thereby, also illustrate the ...

Time resolved donor-acceptor and acceptor-valence band recombination in semiconducting diamond

We report the time resolved photoconductive response of natural and synthetic semiconducting diamond using nanosecond and picosecond laser pulses for 0.4 < δ <4.2 μm. For 0.45 < δ <1.1 μm both acceptor-valence band (A-V) and donor-acceptor (D-A) hole transitions contribute to the photoconductivity; only the former mechanism contributes for 1.1 < δ < 4.2 μm. The A-V recombination has been time resolved to have a characteristic time constant of approximately 150 psec giving a hole recombination cross section of 3 × 10-14cm2. The time resolution was accomplished using 1.06 μm, 20 psec pulses from a Nd:Yag laser in conjunction with an electrical autocorrelation technique. Laser-induced D-V transitions of holes via the acceptors is responsible for the second photoconductivity component; the A-D recombination occurs on a millisecond time scale with the photoconductivity decay being highly nonexponential. The potential use of semi-conducting diamond as an ultrafast infrared detector is briefly discussed.