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Research Of The Temperature-dependent Polarization Coulomb Field Scattering In AlGaN/AlN/GaN Heterostructure Field-Effect Transistors

Posted on:2018-09-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y LiuFull Text:PDF
GTID:1318330512985037Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
The promotion of information technology is trend in the development of the society in today's age.The microelectronics technology has a great impact on the process of the information society.For the development in microelectronics technology,it is directly influenced by the improvement of the performance of the semiconductor devices.Efforts are always being put into reducing the size of the electronic product and mounting to increase the power delivery efficiency.At the same time,people are deeply concerned about whether the electronic products can have the advantages of lowering the energy consumption and pollution emission or do not.The adoption of the emerging semiconductor materials and devices is of great urgency to make electronic products high efficiency,miniaturization,and energy conservation.Due to its excellent properties,such as high temperature,high frequency,and high power microwave and so on,AlGaN/GaN heterojunction field-effect transistors(AlGaN/GaN HFETs),as an important branch of the GaN-based electronics devices,can meet solve the puzzle as mentioned above.Thus,it arouses broad interest at home and abroad.Early in 2010,the AlGaN/GaN HFETs devices utilized commercially have emerged.In recent years,many new types of AlGaN/GaN HFETs devices have been released and applied in more and more fields.High temperature application is one of the important advantages for AlGaN/GaN HFETs.Hence,it is necessary to study the temperature-dependent performance of the devices.So far,there are many researches on temperature-dependent characteristics.However,in the most of these researches many attentions are paid to the evaluation on the degradation of the electrical properties such as the drain-to-source current,transconductance and cut-off frequency,and less attentions to the study on the mechanism of the degradation.Therefore,it is necessary to pay close attention to this problem.It is helpful to improve the performance of the device to make clear the mechanism about the effect of temperature on the performance of the devices.In GaN HFETs,the 2DEG electron mobility is an important parameter for studying the performance of the devices.Scattering mechanism is an important influence factor for electrom mobility.Therefore,the study on the temperature-dependent scattering mechanism is of great importance.In 2007,during the study of the transport mechanism in AlGaN/GaN HFETs,a new kind of scattering mechanism i.e.Polarization Coulomb field scattering(PCF scattering)was first proposed.PCF scattering is originated from the uneven polarization charge distribution along the AlGaN/GaN heterojunction interface.Each process of the device manufacturing and the gate-source or drain-source voltage can have some influences on the uniformity of the strain for the source-to-drain AlGaN barrier layer.Nonuniformity of the strain can lead to the nonuniformity of the polarization charges,which could scatter the 2DEG in the channel of the devices.From 2007 when the polarization Coulomb field scattering was first proposed,to 2014 when the theoretical model of such a new kind of the scattering mechanism was established,PCF scattering has been studying for about 10 years.Even now,the research on the validation and adjustment about theory is making.However,those researches were all made at room temperature.In fact,the influence of PCF scattering on the carrier transport of GaN electronic devices and the electrical properties at different temperatures still needs further study and discussion.Therefore,the main work in this dissertation is to study the influence of the temperature on the 2DEG electron mobility for AlGaN/AlN/GaN heterojunction field-effect transistors(AlGaN/AlN/GaN HFETs)(So far,AlGaN/AlN/GaN HFETs device with the thin AIN intercalation is always adopted for AlGaN/GaN HFETs,therefore the study on the AlGaN/GaN HFETs in this paper are all AlGaN/AlN/GaN HFETs),especially the influence on the PCFs cattering.And the discussions on the influence of PCF scattering on the gate-to-source resistance Rs are further made in the high temperature range.The main conclusions of the dissertation are listed below:1.Temperature-dependent 2DEG electronic system in the AlGaN/AlN/GaN HFETsAlGaN/AlN/GaN HFETs with the drain-to-source length being 100?m and the gate length being 30?m has been prepared.And I-V and C-V measurements for the prepared AlGaN/AlN/GaN HFETs were performed at different temperatures.With the measured temperature-dependent I-V and C-V curves,and by self-consistently solving Schrodinger equation and Poisson equation in MATLAB environment,the influence of temperature on 2DEG electronic system in the AlGaN/AlN/GaN HFETs,involving 2DEG sheet density,the subband structure,the subband occupation and the depth of the triangle quantum well,were investigated.It is shown that as the temperature increases,the triangular quantum well becomes wider and therefore the distribution of the 2DEG electron spreads deep into GaN;and the 2DEG electron sheet density corresponding to the zero gate voltage,the Fermi level,and the polarization of the AlGaN barrier layer at heterojunction interface all decreases.There are two mainly reasons.One reason is that as the temperature increases,the thermal excitation-energy(KBT)of electron could increase.As a result the electron excitation probability for the 2DEG electron in the triangular quantum well would also increase and the quantum characteristics of 2DEG electronic system becomes not obvious.The other reason can be attributed to the difference in thermal expansion coefficient between AlGaN and GaN,which reduces the strain energy and the porlarization electron field in the AlGaN barrier layer.2.Temperature-dependent 2DEG electron mobility in the AlGaN/AlN/GaN HFETs(a)The study on the 2DEG electron mobility in the AlGaN/AlN/GaN HFETs at room temperature.The AlGaN/AlN/GaN HFET with the drain-to-source length being 100?m and the gate length being 40?m has been prepared,and with the measured temperature-dependent I-V and C-V curves,and the theoretical calculation,the relationship between the electron mobility under the gate and the different kinds of scattering mechanisms which include PCF scattering,longitudinal optical(LO)phonon scatterinig,interface roughness(IFR)scattering,dislocation(DIS)scattering,acoustic deformation potential(DP)scattering,and piezoelectric(PE)scattering has also been analyzed and studied quantitatively at room temperature.It is found that the value of the carrier mobility is mainly determined by LO phonon scattering,and the change trend for the carrier mobility with respect to the 2DEG density is mainly determined by PCF scattering.(b)The study on the 2DEG electron mobility in the AlGaN/AlN/GaN HFETs at low temperature.With the measured I-V and C-V curves in the temperature range 100-300K for the fabricated device(The device used in the study at low temperature is the same as that at room temperature except for the heterojunction material system),and combining with Matthiessen's law,the influence of all kinds of scattering mechanisms on 2DEG electron mobility in the AlGaN/AlN/GaN HFETs was investigated.By analyzing the varation of the 2DEG electron mobility with 2DEG sheet density,it is found that in the temperature range 100-200K,PCF scattering plays a more significant role in the impact on the mobility of the carrier in the channel under the gate,and the value of the carrier mobility and the change trend for the carrier mobility with respect to the 2DEG density is mainly determined by PCF scattering.And the role in the impact of PCF scattering on the electron mobility will weaken with increasing temperature.The reason can be attributed to the stronger LOphonon scattering with increasing temperature which makes PCF scattering be relatively weaker in affecting the electron mobility.(c)The influence of the device structure on high temperature 2DEG electron mobility in AlGaN/AlN/GaN HFETs.The AlGaN/AlN/GaN HFETs with the different the drain-to-source length and the gate length(100pm/30?m,100?m/50?m,and 100?m/70?m)were prepared.With the measured I-V and C-V curves in the temperature range 300-500K,the relationship between the electron mobility and 2DEG sheet density at different temperatures were studied.It is shown that in the temperature range 300-500K,PCF scattering still has an important effect on the change trend for the electron mobility with respect to the 2DEG density,and PCF scattering still plays a more significant role in the impact on the mobility of the carrier in the channel under the gate.And particularly for the devices with the samller ratio of gate length to drain-to-source distance(LG/LSD<1/2),even the temperature is up to 500K,the change trend for the carrier mobility with respect to the 2DEG density is still mainly determined by PCF scattering.3.High-temperature-dependent the source-to-gate resistance Rs in the AlGaN/AlN/GaN HFETs(a)The influence of the temperature on the source-to-gate resistance Rs.The AlGaN/AlN/GaN HFET with the drain-to-source length being 100?m and the gate length being 20?m has been prepared,and using the measured temperature-dependent Rs and both C-V and I-V characteristics for the prepared device,the influence of temperature on Rs in the AlGaN/AlN/GaN HFETs was investigated.In particular,the influence of PCF scattering on Rs in the AlGaN/AlN/GaN HFET has been investigated at elevated temperatures.It is found that in the temperature range 300-500K,PCF scattering has an important influence on the parasitic source resistance Rs.And at the same the forward gate-to-source current,the gate-to-soure bias would decrease and so would the magnitude of the additional polarization charge under the gate.As a result the potential of the PCF scattering and the impact of PCF scattering on the Rs would weaken with increasing temperature.And the interaction between the positive additional polarization charges underneath the gate contact and the negative additional polarization charges near the source contact was verified during the variable-temperature study of Rs.(b)The influence of the device structure on the gate-to-source resistance Rs in AlGaN/AlN/GaN HFETs at high temperature.Two AlGaN/AlN/GaN HFETs with the same drain-to-source,the same gate length,and the different gate-to-source length(100?m/20?/10?m,and 100?m/20?m/30?m)were prepared.With the measured temperature-dependent Rs and both C-V and I-V characteristics for the prepared devices,the influence of the device structure on Rs in the AlGaN/AlN/GaN HFETs has been investigated at elevated temperatures.It is found that for the AlGaN/AlN/GaN HFETs devices with the same gate length and the different gate-to-source distance,the shorter the gate-to-source distance,the more influence on the parasitic source resistance Rs the PCF scattering has.This finding is of great benefit to obtain optimized performance of the AlGaN/AlN/GaN HFETs and reduce.the parasitic source resistance Rs.
Keywords/Search Tags:AlGaN/AlN/GaN heterostructure field-effect transistors, two-dimension electron gas, electron mobility, temperature-dependent, polarization Coulomb field scattering
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