A critical requirement for bit patterned media applications is the control and minimization of the switching field distribution (SFD). Here, we use the ΔH(M,ΔM) method to separate dipolar interactions due to neighbor islands from the intrinsic SFD by measuring a series of partial reversal curves of perpendicular anisotropy Co∕Pd based multilayer films deposited onto prepatterned Si substrates. For a 100-nm-period island array the dipolar broadening contributes 22% to the observed SFD. For a 45-nm-period array this value increases to 31%. These results highlight the importance of quantifying long-range dipolar interactions for determining the intrinsic SFD of patterned media.
Electron beam induced current measurements on planar Schottky diodes on undoped GaN grown by metalorganic chemical vapor deposition are reported. The minority carrier diffusion length of 0.28 μm has been measured, indicating minority carrier lifetime of 6.5 ns. The tapping mode atomic force microscopy imaging of the surfaces and scanning electron microscopy of the cross sections have been used to characterize the linear dislocations and columnar structure of the GaN. The possible influence of recombination on the extended defects in GaN on the minority carrier diffusion length and lifetime is discussed, and contrasted to other recombination mechanisms.
We fabricated high standoff voltage ͑450 V͒ Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO 2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm 2 and a saturation current density of 10 Ϫ5 A/cm 2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2Ϯ0.7)ϫ10 6 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects. © 1999 American Institute of Physics. ͓S0003-6951͑99͒02409-2͔Wide band gap materials, primarily SiC and GaN, have recently attracted a lot of interest for applications in high power and high temperature electronics. Although the processing technology for SiC is more mature, GaN offers several advantages. First, there are various device possibilities using GaN/AlGaN heterojunctions which are not available in the SiC system. Second, the availability of cheap and efficient hydride vapor phase epitaxy ͑HVPE͒ growth technology achieving growth rates in excess of 100 m/h, have produced thick, high quality GaN layers on sapphire. 1 Third, by using AlGaN layers, one can take advantage of a larger band gap to achieve higher critical electric fields than in GaN alone.In this study, we focus on the fabrication of high voltage, GaN based Schottky rectifiers and the measurement of the critical field for electric breakdown. The critical field for electric breakdown is one of the most significant parameters in the design and performance of high power devices. It directly influences the required thickness of the standoff region in the Schottky rectifier and bipolar devices, such as the thyristor. Since the thickness of the standoff region sets the resistivity of the device, it will determine power dissipation and maximum current density of the device. 2,3 In previous studies, Schottky diodes have been fabricated on GaN using a variety of elemental metals including Pd and Pt, 4,5 , Au, Cr, and Ni,6,7 , and Mo and W. 8 More details on the metal-GaN contact technology can be found in Ref. 9.In this work, Schottky rectifiers were fabricated on 8-10 m thick GaN layers grown by HVPE on sapphire, where the electron concentration changes with the distance from the GaN/sapphire interface. We carried out conductivity and Hall measurements on a series of HVPE GaN films of varying thickness ranging from 0.07 to 9.2 m, and fitted the data to a two layer model. [10][11][12][13] From the model, we concluded that the GaN films consisted of a low conductivity, low electron concentration, 8-10 m thick top layer on a very thin (Ͻ100 nm), highly conductive, high electron concentration bottom layer. The electron concentrations and mobilities in the thin interface layer and thic...
We have studied molecular beam epitaxy grown GaN films of both polarities using electric force microscopy to detect sub 1 m regions of charge density variations associated with GaN extended defects. The large piezoelectric coefficients of GaN together with strain introduced by crystalline imperfections produce variations in piezoelectrically induced electric fields around these defects. The consequent spatial rearrangement of charges can be detected by electrostatic force microscopy and was found to be on the order of the characteristic Debye length for GaN at our dopant concentration. The electric force microscope signal was also found to be a linear function of the contact potential between the metal coating on the tip and GaN. Electrostatic analysis yielded a surface state density of 9.4Ϯ0.5ϫ1010 cm Ϫ2 at an energy of 30 mV above the valence band indicating that the GaN surface is unpinned in this case. © 1999 American Institute of Physics. ͓S0003-6951͑99͒01223-1͔Nitride based devices have been of great interest in the last few years, notably due to their success in optoelectronics, where lasers and diodes have been demonstrated and successfully commercialized.1 Further applications of nitrides are expected in the arena of high power and high temperature devices, 2-4 as well as solar blind ultraviolet detectors.5 It has been recently demonstrated that the large intrinsic piezoelectric coefficients of GaN and AlN are responsible for a high concentration two-dimensional electron gas at the AlGaN/GaN interface in heterojunction field effect transistors ͑HFET͒.6,7 Other possibilities exist for the enhancement of electric properties of contacts to nitrides by piezoelectric engineering as recently demonstrated in the case of Schottky contacts.8 While most of the recent research has emphasized electronic device aspects of the piezoelectric effect, 6-8 comparatively little work has concentrated on the investigation of fundamental properties and nanoscale characterization of piezoelectrically induced phenomena. One consequence of the piezoelectric effect is that it allows electrostatic force imaging of charge redistribution around defects due to local variations in strain caused by crystalline imperfections. Although the magnitude of the charge density is nonquantitative, electric force microscopy ͑EFM͒ can still provide interesting insight into the nature of defects, the piezoelectric effect in nitrides, as well as measurement of the surface state density and energy. 9,10The gallium nitride layers studied here were grown on c-plane sapphire substrates by radio frequency plasma assisted molecular beam epitaxy. Ga-polar GaN films were nucleated using AlN buffer layers whereas N-polar films were nucleated using a GaN buffer layer. Polarity was determined by reflection high-energy electron diffraction ͑RHEED͒ reconstruction at low temperature, 11 and by ͑KOH͒ etching. 12,13 Other details of the growth conditions are presented elsewhere. 14,15 A variety of different metals were used for coating atomic force microscope ͑AF...
We report on electron beam induced current and current-voltage (I -V) measurements on Schottky diodes on p-type doped GaN layers grown by metal organic chemical vapor deposition. A Schottky barrier height of 0.9 eV was measured for the Ti/Au Schottky contact from the I -V data. A minority carrier diffusion length for electrons of (0.2Ϯ0.05) m was measured for the first time in GaN. This diffusion length corresponds to an electron lifetime of approximately 0.1 ns. We attempted to correlate the measured electron diffusion length and lifetime with several possible recombination mechanisms in GaN and establish connection with electronic and structural properties of GaN. © 1998 American Institute of Physics. ͓S0003-6951͑98͒03848-0͔The wide band gap semiconductors GaN and AlGaN are already established materials for light emitting diodes and lasers, 1 and have recently attracted a lot of interest for applications in high power and high temperature electronics. 2 Some of the most significant parameters influencing the design and performance of both unipolar and bipolar high power devices are the critical field for electric breakdown and the transport parameters, such as minority carrier diffusion lengths and lifetimes, for both holes and electrons. Correlation of these parameters with material properties is important for succesful development of power electronics systems based on the nitrides. Minority carrier diffusion lengths and lifetimes are critical parameters for the performance of thyristor switches and other bipolar devices. 3,4 Larger hole lifetimes in the n-type standoff layer of thyristors lead to smaller ON-state voltages and therefore smaller power dissipation and larger maximum current densities. 3,4 The electron diffusion length is important because it determines the range of suitable thicknesses for the p-type injection layer in bipolar structures. In this study we report a measurement of the electron diffusion length and estimate the electron lifetime as a minority carrier in GaN.We fabricated Schottky diodes on Mg-doped GaN/ sapphire layers grown by metal organic chemical vapor deposition ͑MOCVD͒. The experiments were performed on samples from two commercial vendors. For both samples the hole concentration measured by Hall measurements was approximately (1 -4)ϫ10 17 cm Ϫ3 , and the hole mobility was approximately 5 cm 2 /V s. Prior to metal deposition, the GaN surfaces were cleaned with organic solvents, dipped in HF:H 2 O ͑1:10͒, rinsed in deionized water, then blown dry with nitrogen gas. Contact metals were sputtered in a chamber with background pressure of 2ϫ10 Ϫ8 Torr and patterned to produce Schottky contacts as well as large-area ohmic contacts. A Ni/Au ͑200 Å/1500 Å͒ metallization scheme was used for the ohmic contacts, while Ti/Au was used for the Schottky contacts.Current-voltage characteristics were measured at room temperature with an HP 4156 parameter analyzer and are shown in Fig. 1. From these measurements we obtained a barrier height of ⌽ Bp ϭ0.9 eV. Since the reported barrier heigh...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.