摘要:

The role of localized defect centers and continuous gap states distribution in photoluminescence, photoconductivity, and photoresponse time dependence of diamond films have been analyzed for different film morphology and grain orientations. Sharp spectroscopic features related to impurity centers or broad components associated with continuous distribution of gap states prevail in the spectra depending on film microstructure and deposition technique. It is shown that defects, either localized or continuously distributed, reduce carrier lifetimes and slow down carrier transport by trapping effects. The observation of metastability effects after UV illumination giving an increase of subgap photoresponse is also reported.

ISSN:1071-1023    

DOI:10.1116/1.590043

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Optical properties ofin situEr-doped Si epilayers grown by molecular beam epitaxy at low temperatures (<450 °C), using oxygen and fluorine as codopants, are studied using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Sharp and intense Er-related PL is observed at low temperatures from the as-grown Si epilayers with Er concentrations up to5×1019 cm−3.The structure of the dominant optically active Er centers is shown to be dependent of the codopants used and can essentially be modified by postgrowth thermal annealing. The chemical nature of the codopants as well as postgrowth treatments have only a minor effect on the thermal quenching of Er-related emissions. Thermal quenching of the Er-related PL and EL is shown to occur with a similar activation energy suggesting the same quenching mechanism may be involved for both processes. The observed higher EL efficiency at elevated temperatures is tentatively attributed to the higher concentration of excited Er ions under impact ionization conditions (EL).

ISSN:1071-1023    

DOI:10.1116/1.590044

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

ThickSi0.9Ge0.1relaxed layers grown by chemical vapor deposition on Si(100) oriented substrates are investigated by photoluminescence (PL) spectroscopy. Resolved excitonic near-band-gap luminescence is observed in as-grown and hydrogen treated samples. Phonon assisted transitions are also well identified. The effect of hydrogenation is to enhance the luminescence related to the near-band gap. This enhancement is correlated with a quenching in the dislocation related PL especially for the D3–D4 bands and the T band. This indicates that hydrogenation passivates radiative centers inside dislocation cores which are responsible, beside nonradiative channels, for the quenching of SiGe band-gap edge luminescence.

ISSN:1071-1023    

DOI:10.1116/1.590045

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

High leakage currents at the base-collector junction of heterojunction bipolar transistors have been mentioned by several authors. In this article, we compare two pre-epitaxy cleaning procedures which both allow smooth epitaxy without any extended defects. Using our initial cleaning procedure, we obtained leakage current values in the range of the published results. We show that our results were consistent with the presence of defects induced by the low-energy reactive ion etching involved in this procedure. In contrast, we obtain a very significant reduction of the leakage current using our new all-wet chemical cleaning.

ISSN:1071-1023    

DOI:10.1116/1.590046

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Deep-level transient spectroscopy (DLTS) measurements have been performed on SiGe heterojunction bipolar transistors fabricated in a complementary metal–oxide–semiconductor compatible polysilicon self-aligned process. A detailed study of the emitter–base capacitance transient as a function of the filling pulse parameters and transistor geometry has shown that the deep levels are correlated to point defects uniformly distributed along the emitter–base junction periphery and attributed to the reactive ion etching (RIE) process. The observed deep electron traps are located at 0.6 eV below the conduction band with a capture cross section of10−17 cm2.In order to confirm that the observed defects were not correlated to the SiGe base material, a similar investigation was carried out on mesa devices grown in the same reactor with the same intrinsic structure but whose emitter–base active zone did not suffer RIE. In these devices, a new electron trap with an activation energy of 0.38 eV and a capture cross section of10−19 cm2is detected. This trap is sensitive to the electric field as in the case of the self-aligned structure, but a detailed study has shown that it has a different origin. Finally, the first peripheral electron trap atEc−0.6 eVis not observed in mesa devices in good agreement with our first hypothesis.

ISSN:1071-1023    

DOI:10.1116/1.590047

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We show that the incorporation of low carbon concentration(<1020cm−3)within the SiGe region of SiGe heterobipolar transistors (HBT) can significantly suppress boron outdiffusion caused by later processing steps. We were able to obtainfT/fmax⩾50 GHz for a simple SiGe:C transistor with a box-shaped Ge profile. Comparing the high frequency performance of molecular beam epitaxy grown SiGe:C HBTs with identical SiGe HBTs, we found an increase infTandfmaxby a factor of more than 2. The static characteristics for SiGe:C HBTs demonstrate that the transistors should be suitable for circuit applications. Process margins for SiGe HBT technology are shown to be relaxed due to C incorporation. The dramatic reduction of B diffusion in C-rich Si under conditions of point defect equilibrium is attributed to a reduction of the concentration of interstitials available for the B diffusion.

ISSN:1071-1023    

DOI:10.1116/1.590048

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Pure Ge/Si heterostructures were epitaxially grown on Si in order to obtain Si-integrated photodetectors in the near-infrared region. Samples grown with different procedures are compared. Graded buffer layers ofSi1−xGexwithxvariable as a function of depth were grown in order to relax the stress. On top of these, pure Ge layers were grown. The mechanism of strain relaxation has been investigated by transmission electron microscopy and the surface morphology by scanning electron microscopy. The results on different samples are discussed and compared in terms of structural properties and photoresponse, in an attempt to correlate structural defects to photodetector efficiency.

ISSN:1071-1023    

DOI:10.1116/1.590049

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We have studied wet thermal oxidation between 700 and 1100 °C of strainedSi1−yCy(0⩽y⩽0.02)layers grown by molecular beam epitaxy on Si(001) substrates. The oxidation kinetics and the refractive indices of the oxides grown onSi1−yCywere monitored by ellipsometry. They show no significant differences in comparison with oxides grown on silicon. Secondary ion mass spectroscopy and x-ray photoelectron spectroscopy reveal the appearance of carbon in the oxide. To find an appropriate temperature window for oxidation, we investigated the underlyingSi1−yCylayers after oxidation by infrared absorption measurements. We observed a decrease of the substitutional carbon concentration for oxidation temperatures higher than 800 °C. Thus, only a small temperature window for the growth of good thermal oxide onSi1−yCylayers is available. Infrared absorption measurements on the oxide vibrational modes reveal a small influence of the carbon concentration on the structural quality of the oxide.

ISSN:1071-1023    

DOI:10.1116/1.590050

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Atomic force microscopy topography and power spectral density analysis of the recorded images were used to obtain a thorough characterization of the morphological modifications determined by laser processing ofSi(1−x)Gex/Si(100) structures grown by ultrahigh vacuum chemical vapor deposition (CVD). Two irradiation modalities were considered. In the first case, several samples differing in alloy film thickness and morphology were irradiated by KrF laser pulses at 248 nm after the CVD growth. Alternatively, the laser pulses were used to assist the CVD growth itself. In both cases laser irradiation determined primarily a severe smoothing of the surface roughness. However for the post-growth irradiation the achieved flatness was strictly dependent on the initial surface features (i.e., roughness and grain dimensions). The comparison between the results obtained in the two irradiation modalities demonstrated that, as far as surface flatness is concerned, laser-assisted deposition results a superior technique, since it allows the achievements of structureless surfaces, with roughness as low as 0.3 nm.

ISSN:1071-1023    

DOI:10.1116/1.590051

出版商:American Vacuum Society    

年代:1998

数据来源: AIP