Performance of La2O3/InAlN/GaN metal—oxide—semiconductor high electron mobility transistors

We report on the performance of La2O3/InAlN/GaN metal-oxide-semiconductor high electron mobility transistors(MOSHEMTs) and InAlN/GaN high electron mobility transistors(HEMTs).The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device,while the gate leakage current in the reverse direction could be reduced by four orders of magnitude.Compared with the HEMT device of a similar geometry,MOSHEMT presents a large gate voltage swing and negligible current collapse.     

Improved crystal quality of GaN film with the in-plane lattice-matched Ino.17Alo.s3N interlayer grown on sapphire substrate using pulsed metal-organic chemical vapor deposition

We report on an improvement in the crystal quality of GaN film with an Ino.17Alo.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations （TDs） in GaN film with the InA1N interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy （TEM） measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InA1N interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InA1N interlayer. Atomic force microscopy measurement shows that the InA1N interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InA1N interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.     

The degradation mechanism of an AlGaN/GaN high electron mobility transistor under step-stress

Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AlGaN/GaN high electron mobility transistor(HEMT).It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments.We postulate that defects may be randomly induced within the AlGaN barrier by the high electric field during each voltage step.But once the critical voltage is reached,the trap concentration will increase sharply due to the inverse piezoelectric effect.A leakage path may be introduced by excessive defect,and this may result in the permanent degradation of the AlGaN/GaN HEMT.     

Luminescence of a GaN grain with a nonpolar and semipolar plane in relation to microstructural characterization

We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask.Transmission electron microscopy,scanning electron microscopy,and Raman spectroscopy are used to reveal the effect of SiN on the overgrown a-plane GaN growth.The SiN layer effectively terminates the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN regrowth through the interlayer,resulting in the window region shrinking from a rectangle to a "black hole".Furthermore,strong yellow luminescence(YL) in the nonpolar plane and very weak YL in the semipolar plane on the GaN grain is revealed by cathodoluminescence,suggesting that C-involved defects are responsible for the YL.     

Effects of the strain relaxation of an AlGaN barrier layer induced by various cap layers on the transport properties in AlGaN/GaN heterostructures

The strain relaxation of an AlGaN barrier layer may be influenced by a thin cap layer above, and affects the transport properties of AlGaN/GaN heterostructures. Compared with the slight strain relaxation found in AlGaN barrier layer without cap layer, it is found that a thin cap layer can induce considerable changes of strain state in the AlGaN barrier layer. The degree of relaxation of the AlGaN layer significantly influences the transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. It is observed that electron mobility decreases with the increasing degree of relaxation of the AlGaN barrier, which is believed to be the main cause of the deterioration of crystalline quality and morphology on the AlGaN/GaN interface. On the other hand, both GaN and AlN cap layers lead to a decrease in 2DEG density. The reduction of 2DEG caused by the GaN cap layer may be attributed to the additional negative polarization charges formed at the interface between GaN and AlGaN, while the reduction of the piezoelectric effect in the AlGaN layer results in the decrease of 2DEG density in the case of AlN cap layer.     

Low specific on-resistance GaN-based vertical heterostructure field effect transistors with nonuniform doping superjunctions

A novel Ga N-based vertical heterostructure field effect transistor(HFET) with nonuniform doping superjunctions(non-SJ HFET) is proposed and studied by Silvaco-ATLAS,for minimizing the specific on-resistance(R_(on)A) at no expense of breakdown voltage(BV).The feature of non-SJ HFET lies in the nonuniform doping concentration from top to bottom in the n-and p-pillars,which is different from that of the conventional Ga N-based vertical HFET with uniform doping superjunctions(un-SJ HFET).A physically intrinsic mechanism for the nonuniform doping superjunction(non-SJ) to further reduce R_(on)A at no expense of BV is investigated and revealed in detail.The design,related to the structure parameters of non-SJ,is optimized to minimize the R_(on)A on the basis of the same BV as that of un-SJ HFET.Optimized simulation results show that the reduction in R_(on)A depends on the doping concentrations and thickness values of the light and heavy doping parts in non-SJ.The maximum reduction of more than 51% in R_(on)A could be achieved with a BV of 1890 V.These results could demonstrate the superiority of non-SJ HFET in minimizing R_(on)A and provide a useful reference for further developing the Ga N-based vertical HFETs.     

Low power fluorine plasma effects on electrical reliability of AlGaN/GaN high electron mobility transistor

The new electrical degradation phenomenon of the AlGaN/GaN high electron mobility transistor(HEMT) treated by low power fluorine plasma is discovered. The saturated current, on-resistance, threshold voltage, gate leakage and breakdown voltage show that each experiences a significant change in a short time stress, and then keeps unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. These results suggest that the low power fluorine implant ion stays in an unstable state. It causes the electrical properties of AlGaN/GaN HEMT to present early degradation. A new migration and degradation mechanism of the low power fluorine implant ion under the off-stress electrical stress is proposed. The low power fluorine ions would drift at the beginning of the off-state stress, and then accumulate between gate and drain nearby the gate side. Due to the strong electronegativity of fluorine, the accumulation of the front fluorine ions would prevent the subsequent fluorine ions from drifting, thereby alleviating further the degradation of AlGaN/GaN HEMT electrical properties.     

Improvement in a-plane GaN crystalline quality using wet etching method

Nonpolar （1120） GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 （high） phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 （high） peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 （high） peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.     

Germanium PMOSFETs with Low-Temperature Si2H6 Passivation Featuring High Hole Mobility and Superior Negative Bias Temperature Instability

We investigate negative bias temperature instability （NBTI） on high performance Ge p-channel metal-oxide- semiconductor field-effect transistors （pMOSFETs） with low-temperature Si2H6 passivation. The Ge pMOSFETs exhibit an effective hole mobility of 311 cm2/V.s at an inversion charge density of 2.5 × 1012 cm^-2. NBTI characterization is performed to investigate the linear transconductance （GM,lin） degradation and threshold voltage shift （△VTH） under NBT stress. Ge pMOSFETs with a lOyr lifetime at an operating voltage of -0.72 V are demonstrated. The impact of the Si2H6 passivation temperature is studied. As the passivation temperature increases from 350℃ to 550℃, the degradation of NBTI characteristics, e.g., GM,lin loss, △VTH and an operating voltage for a lifetime of lOyr, is observed.     

Optimization and Finite Element Analysis of the Temperature Field in a Nitride MOCVD Reactor by Induction Heating

A susceptor structure with a ring channel for a vertical metalorganic chemical vapor deposition reactor by induction heating is proposed. Thus the directions of heat conduction are changed by the channel, and the channel makes the heat in the susceptor redistribute. The pattern of heat transfer in this susceptor is also analyzed. In addition, the location and size of the channel in the susceptor are optimized using the finite element method. A comparison between the optimized and the conventional susceptor shows that the optimized susceptor not only enhances the heating efficiency but also the uniformity of temperature distribution in the wafer, which contributes to improving the quality of the film growth.