Yeon-Ho Kil

Nanoscale dry etching of germanium by using inductively coupled CF4 plasma

The nanoscale dry etching of germanium was investigated by using inductively coupled CF4 plasma and electron-beam lithography. The optimal dose of PMMA as E-beam lithography resist was ∼200 mC/cm2. When ICP Power was 200W, CF4 gas flow rate was 40 sccm, and process pressure was 20 mTorr, it had a smooth surface and good etch rate. The etching selectivity of Ge wafer to PMMA resist was as low as ∼1.5. Various sub-100 nm dry-etching patterns have been obtained. SEM pictures showed good profile qualities with a smooth etching sidewall and ultrasmall etching features.

Temperature Dependent Current Transport Mechanism in Graphene/Germanium Schottky Barrier Diode

We have investigated electrical properties of graphene/Ge Schottky barrier diode (SBD) fabricated on Ge film epitaxially grown on Si substrate. When decreasing temperature, barrier height decreased and ideality factor increased, implying their strong temperature dependency. From the conventional Richardson plot, Richardson constant was much less than the theoretical value for n-type Ge. Assuming Gaussian distribution of Schottky barrier height with mean Schottky barrier height and standard deviation, Richardson constant extracted from the modified Richardson plot was comparable to the theoretical value for n-type Ge. Thus, the abnormal temperature dependent Schottky behavior of graphene/Ge SBD could be associated with a considerable deviation from the ideal thermionic emission caused by Schottky barrier inhomogeneities.

Correlation of reverse leakage current conduction mechanism and electrostatic discharge robustness of transient voltage suppression diode

Five transient voltage suppression (TVS) diodes with breakdown voltages (BV) of 6, 7, 11, 13 and 15 V have been developed using low-temperature (LT) epitaxy technology and an LT fabrication process. The electrostatic discharge (ESD) performance and temperature dependency of reverse leakage current are investigated by applying the IEC61000-4-2 (IEC) standard and an I-V-T analysis. The TVS diodes exhibited excellent ESD robustness, exceeding the standard ESD requirement of IEC level 4, 8 kV in contact discharge, while also maintaining the reverse leakage current level below 10−9 A. Excellent ESD performance was found to be relevant for lower breakdown voltage TVS diodes. The reverse leakage currents showed substantial changes in thermal activation energy from 0.43 to 0.6 eV with respect to BV control from 6 to 15 V. The increased activation energy at high BV was attributed to the transition of the conduction mechanism from tunneling mode to generation-recombination mode. The reduction of reverse leakage current from a generation-recombination to tunneling conduction mechanism is expected to improve the ESD performance of TVS diodes.

Growth and characterization of Si1−xGetx QDs on Si/Si0.8Ge0.2 layer

Si1−xGetx QDs structures were grown onto Si/Si0.8Ge0.2 layer using RPCVD system. Ge composition in Si1−xGetx QDs was determined as about 30% and 40%. Three peaks are observed in Raman spectrum, which are located at about 520, 410, and 295 cm−1, corresponding to the vibration of Si-Si, Si-Ge, and Ge-Ge phonons, respectively, and the Si1−xGetx QDs related peak was located at 490 cm−1. The PL spectrum that originates from the radiative recombinations came from the Si substrate, the Si0.8Ge0.2 layer and Si1−xGetx QDs. For Si1−xGetx QDs, the transition peaks related to the QDs region observed in the photocurrent spectrum were preliminarily assigned to electron-heavy hole (e-hh) and electron-light hole (e-lh) fundamental excitonic transitions.

Early stage of heteroepitaxial Ge growth on Si(100) substrate with surface treatments using inductively coupled plasma (ICP)

(Received June 27, 2011)(Revised July 13, 2011)(Accepted July 15, 2011)Abstract We have investigated the effect of inductively coupled plasma (ICP) treatment on the early growth stage ofheteroepitaxial Ge layers grown on Si(100) substrates using low pressure chemical vapor deposition (LPCVD). The Si(100)substrates were treated by ICP process with various source and bias powers, followed by the Ge deposition. The ICPtreatment led to the enhancement in the coalescence of Ge islands. The growth rate of Ge on Si(100) with ICP surfacetreatment is about 5 times higher than that without ICP surface treatment. A missing dimer caused by the ICP surfacetreatment can act as a nucleation site for Ge adatoms, which could be responsible for the improvement in growth behaviorof Ge on Si(100) substrates.Key wordsICP, SEM, Island, Coalescence, LPCVD, Germanium, Silicon, missing dimer

Ge1−xSnx/Ge heterostructure infrared photodetector

We report the optoelectronic characterization of Ge_2-xSn_x/Ge heteroj unction infrared (IR) photodetectors fabrication on Si substrate using rapid thermal chemical vapor deposition (RTCVD) with Ge₂H₆ and SnCl₄ precursors and in a CMOS compatible process. We obtained that Sn contents in Ge_1-xSn_x. epitaxial layer ~5.9%. The surface roughness root mean square (RMS) were 1.2 nm. The leakage current of a device as low as 0.7 μA at 1 V and leakage current reduced as device size decrease. At 1550 nm wavelength, the responsivity of the Ge_1-xSn_x/Ge devices was estimated to be 54 mA/W was measured for a bias of 2 V, without an optimal antireflection coating. Fabricated device shows practicability for optoelectronic applications in the extended IR wavelength regime.

Selective Chemical Wet Etching of Si 0.8 Ge 0.2 /Si Multilayer

We investigate the effect of the ageing time and etching time on the etching rate of SiGe mixed etching solution, namely 1 vp HF (6%), 2 vp H₂O₂ (30%) and 3 vp CH₃COOH (99.8%). For this etching solution, we found that the etch rate of SiGe layer is saturated after the ageing time of 72 hours, and the selectivity of Si 0.8 Ge 0.2 layer and Si layer is 20:1 at ageing time of 72 hours. The collapse was appeared at the etching time of 9min with etching solution of after saturation ageing time.

Optical Property of Si0.8Ge0.2/Si Multilayer Grown by Using RPCVD

We have investigated the of Si0.8Ge0.2/Si multi-layer structures grown directly onto Si (001) substrates using reduced pressure chemical vapor deposition (RPCVD) system. The Si substrates were cleaned through a normal cleaning procedure before the Si0.8Ge0.2/Si multi-layer growth. The growth of the Si0.8Ge0.2/Si multi-layer was then commenced by switching the SiH4 and GeH4 (1.5% diluted in H2) into reactor. The flow rates of SiH4 and GeH4 were changed from 10 to 100 sccm and from 40 to 300 sccm, respectively. The flow rate of H2 was fixed at 10slm. The growth temperatures were 600°C with a growth rate of 3.2nm/min for the Si0.8Ge0.2 layer and 600°C for the Si layer with a growth rate of 3.8nm/min. Finally, the layered structures were completed by depositing a 40 nm Si cap layer. Fig. 1 shows cross-sectional TEM image of Si0.8Ge0.2/Si multi-layer with Si layer thickness of 40 nm and Si0.8Ge0.2 layer thicknesses of 20, 40 and 60 nm, respectively. Fig. 2 shows the XRD patterns of the Si0.8Ge0.2/Si multi-layer and Ge/Si layer. The XRD peak position of the SiGe(004) plane shifts to the Ge(004) plane. This indicates that the Ge concentration in the SiGe layer is 20%. Fig. 3 shows Raman spectra of the Si0.8Ge0.2/Si multi layer taken in Raman setup at a temperature of 300 K. Strong substrate peak is observed in the Raman spectra at 520 cm, denoted as SiLO–TO which corresponds to the longitudinal optical–transverse optical (LO-TO) phonon. Three peaks corresponding to the vibration of Si-Si, SiGe, and Ge-Ge phonons are observed at about 510, 410, and 300 cm, respectively. Temperature dependence of photoluminescence spectra of Si0.8Ge0.2/Si multi-layer was measured from 4 to 300 K. Figure 4 shows photoluminescence spectrum for Si0.8Ge0.2/Si multi-layer at a temperature of 4 K. This spectrum originates from the radiative recombinations both from the Si substrate and the Si0.8Ge0.2/Si multi-layer. Peaks labeled as SiGe(NP) and SiGe(TO) correspond to the no-phonon (NP) and TO-phonon assisted transition from Si0.8Ge0.2/Si multi-layer. Band-edge emission (SiGe(NP)) was clearly observed from the Si0.8Ge0.2/Si multi-layer grown by using RPCVD. From the position (or energy) of these peaks, the Ge concentration at the apex of the Si1-xGex profile can be derived. A value of 0.20 was found for this sample. Figure 5 shows the photoluminescence spectra of temperature dependence. Fig. 6 shows the photocurrent spectrum of the Si0.8Ge0.2/Si multi-layer taken in photocurrent setup at a temperature of 10 K. The photocurrent spectrum was dominated by the QWs related transition that corresponding to the transitions of the electron-heavy hole sub-band (e-hh) and electron-light hole sub-band (e-lh).