Guangze Zhang

GeSn p-i-n photodetector for all telecommunication bands detection

Using a 820 nm-thick high-quality Ge0.97Sn0.03 alloy film grown on Si(001) by molecular beam epitaxy, GeSn p-i-n photodectectors have been fabricated. The detectors have relatively high responsivities, such as 0.52 A/W, 0.23 A/W, and 0.12 A/W at 1310 nm, 1540 nm, and 1640 nm, respectively, under a 1 V reverse bias. With a broad detection spectrum (800-1800 nm) covering the whole telecommunication windows and compatibility with conventional complementary metal-oxide-semiconductors (CMOS) technology, the GeSn devices are attractive for applications in both optical communications and optical interconnects.

Germanium–Tin (GeSn) p-Channel MOSFETs Fabricated on (100) and (111) Surface Orientations With Sub-400

In this letter, we report the first study of the dependence of carrier mobility and drive current I_Dsat of Ge_0.958Sn_0.042 p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) on surface orientations. Compressively strained Ge_0.958Sn_0.042 channels were grown on (100) and (111) Ge substrates. Sub-400°C Si₂H₆ treatment was introduced for the passivation of the GeSn surface prior to gate stack formation. Source/ drain series resistance and subthreshold swing S were found to be independent of surface orientation. The smallest reported S of 130 mV/decade for GeSn pMOSFETs is achieved. The (111)-oriented device demonstrates 13% higher IDsat over the (100)oriented one at a V_GS-V_TH of -0.6 V and V_DS of -0.9 V. We also found that GeSn pMOSFETs with (111) surface orientation show 18% higher hole mobility than GeSn pMOSFETs with (100) orientation.

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Surface-illuminated GeSn p-i-n photodetectors (PDs) with Ge0.964Sn0.036 active layer on Ge substrate were fabricated. Photodetection up to 1.95 μm is achieved with a responsivity of 0.13 A/W. High responsivities of 0.56 and 0.71 A/W were achieved under a reverse bias voltage of 3 V at 1640 and 1790 nm, respectively. A low dark current of 1.08 μA was obtained at a reverse bias of 1 V with a diameter of 150 μm, which corresponds to a current density of 6.1 mA/cm2. This value is among the lowest dark current densities reported among GeSn PDs.

Passivation

We measure second-harmonic generation from arrays of sub-wavelength apertures in transmission using fundamental input at 800 nm. Lattice arrangements include disordered, Penrose (quasi-periodic or aperiodic), and square (periodic). Strong angular dependence of SHG is observed, with maxima located at angular positions that roughly correspond to incidence angles of extraordinary optical transmission (EOT) for the fundamental. In addition, even at incidence normal to the sample, strong secondary maxima are observed at off-normal scattering angles for the arrangements with higher degree of order. Breaking the inversion symmetry of the aperture allows second harmonic peaks at normal incidence and detection. These measurements help to resolve the role that symmetry plays in second-harmonic generation from arrays of apertures.

High-responsivity GeSn short-wave infrared p-i-n photodetectors

In this work, we report the first demonstration of GeSn pTFET. Good device characteristics were obtained. This may be attributed to direct BTBT, high hole mobility in the GeSn channel, and the formation of abruptly and heavily doped N+ source. The ION performance can be improved with further device optimization.

Second-harmonic emission from sub-wavelength apertures: Effects of aperture symmetry and lattice arrangement

In this paper, we report the worlds first germanium-tin (GeSn) channel nMOSFETs. Highlights of process module advances are: low temperature (400 °C) process for forming high quality n+/p junction with high dopant activation and reduced dopant diffusion; interface engineering achieved with GeSnO2 interfacial layer (IL) between high-k gate dielectric and GeSn channel. A gate-last process was employed. The GeSn nMOSFET with GeSnO2 IL demonstrates a substantially improved SS in comparison with Ge control, and an ION/IOFF ratio of 104.

Towards direct band-to-band tunneling in P-channel tunneling field effect transistor (TFET): Technology enablement by Germanium-tin (GeSn)

Cracking behaviors in nanoscale Cu/Ta multilayers bonded to polyimide substrates have been investigated by uniaxial tensile tests. Experimental results show that cracks originate from the localized deformation regions associated with aligned grain boundaries. Microscopical observations suggest that the alignment of the grain boundaries is caused by local grain boundary sliding and grain rotation, which resulted in the in-plane and out-of-plane cooperative movements of the grains in the multilayers. From the localized damage regions, shear fracture in the through-thickness direction occurred in the nanoscale Cu/Ta multilayer.

Strained germanium-tin (GeSn) N-channel MOSFETs featuring low temperature N+/P junction formation and GeSnO2 interfacial layer

AGe_0.976Sn_0.024 n⁺/p diode was formed using phosphorus ion (P⁺) implant and rapid thermal annealing at 400°C. Activation of P in Ge typically requires high temperatures (e.g., 700°C), and it was found that this is not needed in the presence of a small amount of Sn. A high forward bias current of 320 A/cm² at -1 V is achieved for the Ge_0.976Sn_0.024n⁺/p diode. This is four times higher than that of the Ge n⁺/p control diode, which received the same P⁺ implant but activated at 700°C. The n⁺-GeSn region has a high active dopant concentration of 2.1 × 10¹⁹× cm^-3, much higher than that in the Ge control. The increased active dopant concentration in GeSn reduces the width of the tunneling barrier between the Al contact and the n⁺-GeSn and increases the forward bias diode current. Enhancement of P activation in Ge_0.976Sn_0.024 could possibly be as a result of passivation of vacancies in the Ge lattice due to Sn atoms.

Origin of cracking in nanoscale Cu/Ta multilayers

Optical gain characteristics of Ge1?xSnx are simulated systematically. With an injection carrier concentration of 5 ? 1018/cm3 at room temperature, the maximal optical gain of Ge0.922Sn0.078 alloy (with n-type doping concentration being 5 ? 1018/cm3) reaches 500?cm?1. Moreover, considering the free-carrier absorption effect, we find that there is an optimal injection carrier density to achieve a maximal net optical gain. A double heterostructure Ge0.554Si0.289Sn0.157/Ge0.922Sn0.078/Ge0.554Si0.289Sn0.157 short-wave infrared laser diode is designed to achieve a high injection efficiency and low threshold current density. The simulation values of the device threshold current density Jth are 6.47?kA/cm2 (temperature: 200?K, and ? = 2050?nm), 10.75?kA/cm2 (temperature: 200?K, and ? = 2000?nm), and 23.12?kA/cm2 (temperature: 300?K, and ? = 2100?nm), respectively. The results indicate the possibility to obtain a Si-based short-wave infrared Ge1?xSnx laser.

Germanium–Tin

Epitaxial Ge1−xSnx alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100) substrate, a high crystalline quality strained Ge0.97Sn0.03 alloy is grown, with a χmin value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100) substrate, strain-relaxed Ge0.97Sn0.03 alloys are epitaxially grown at 150 °C-300 °C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and device performance.