Padmaja Nagaiah

Strained Quantum Wells for P-channel InGaAs CMOS

We present experimental results on the effect of strain on hole transport in InGaAs quantum well (QW) structures. Indium content was varied from lattice matched to high compressive stress in InGaAs/InP QW and the transport properties were analyzed at various temperatures (T = 77-300 K) using Hall measurements. The effect of QW thickness (4-20 nm) on hole transport is also presented. The current best results include room temperature mobility and sheet resistance of 390 cm 2 /V-s and 8500 Ω/sq., respectively. It was observed that the mobility had a T -1.8 dependence indicating similar scattering mechanism in almost all of the samples with prominent mechanism being due to interface and barrier scattering. Further optimization of p-channel for InGaAs CMOS needs to be performed using the above results as guidelines.

A III-V field effect transistor (FET) with hafnium oxide gate dielectric for the detection of deoxyribonucleic acid (DNA) hybridization

Field-portable DNA biosensors have the potential to greatly improve diagnosis of disease, forensic DNA analysis, food safety monitoring, and biowarfare detection. These sensors detect hybridization of complementary strands of DNA, one immobilized onto the sensor substrate and the other free in solution. Most DNA sensors suffer from lack of portability or the inability to process large numbers of samples in parallel. Field effect transistor (FET) based DNA sensors, which detect hybridization by sensing negative charges on target DNA through the field effect, have the potential for both high throughput and portable detection [1].

Mobility and scattering mechanisms in buried InGaSb quantum well channels integrated with in-situ MBE grown gate oxide

InGaSb material family with its higher hole transport properties are potential candidates for group III-V CMOS circuits. Understanding of the dominant scattering mechanisms is crucial for the development of future high speed, low power device applications. We present Hall mobility data of p-type InGaSb quantum well (QW) channels and derive the dominant scattering mechanisms related to the interface and trapped charges that degrade mobility in these structures.

Improvement of the GaSb/Al 2 O 3 interface using a thin InAs surface layer

A major challenge in fabricating a high mobility (In)GaSb based transistor is reducing the density of trap states (D it ) at the III-V/high-k interface [1]. Unoccupied surface bonds react with ambient oxygen and create energy levels within the GaSb bandgap which limit Fermi level movement and degrade sub-threshold slope. InGaAs and other As-rich surfaces have been thoroughly investigated and exhibit significant trap state reduction with Ammonium Sulfide passivation and further native oxide reduction when exposed to TMA precursor used in ALD [2,3]. Interface engineering of GaSb is accomplished using an epitaxially grown 2nm InAs top layer. This GaSb/InAs gate stack has shown immense improvement in C-V characteristics and a significant reduction of D it at the III-V/high-k interface.