A kind of highly reliable A lGaN/GaN heterostructure design methods
Technical field
The present invention relates to a kind of under-relaxation, highly reliable AlGaN/GaN heterostructure design methods, belong to semiconductor
Heterogeneous structure material and device arts.
Background technology
GaN material as third generation semiconductor material with wide forbidden band representative, it is great in terms of high temperature microwave high power device
Application advantage.The prominent characteristic that nitride is different from other compound semiconductor materials is that this makes with very strong polarity effect
Conventional AlGaN/GaN heterojunction structures are up to 1 × 10 even in undoped with the case of, can also obtaining surface density13cm-2Two dimension
Electron gas, a magnitude higher than traditional GaAs systems.AlN insert layer technologies are further introduced on this basis, that is, are formed
AlGaN/AlN/GaN heterojunction structures, can not only strengthen polarity effect, improve two-dimensional electron gas, and due to AlN pairings
The shielding action of golden disordered chain, can also significantly improve two-dimensional electron gas mobility.
In recent years, with GaN material and the continuous maturation of device technology, microwave power device performance, which is obtained, significantly to be carried
Rise, engineering application process is also promoted lasting, and the long-term reliability of GaN HEMT devices becomes and limits its big rule at present
The main bottleneck of mould application, wherein the defect as caused by stress is to cause one of principal element of component failure.With Lattice Matching
AlGaAs/GaAs HEMT heterojunction structures it is different, AlGaN/(AlN)/ GaN heterojunction structures are a kind of counterfeit distribution structure, AlN crystalline substance
Lattice constant is smaller than GaN, and this AlGaN layer for be grown on GaN cushions has tensile strain and increases with Al components and increase.
On the one hand, by strain caused by piezoelectric polarization can REINFORCED Al GaN/GaN interfaces positive polarisation charge, be conducive to two-dimensional electron gas dense
The raising of degree, on the other hand, straining senior general causes lattice relaxation, and thus caused defect will cause device performance and reliability
Decline, be the most typically the inverse piezoelectric effect proposed by MIT research groups.Because AlGaN potential barrier exists necessarily in itself
Strain, under strong electric field action, strain further increases simultaneously more than critical value so that lattice relaxation is simultaneously leaked near side in grid pin
Lattice defect or crackle are produced, so as to cause device performance degeneration or even failure.At present, how substantial amounts of work is concentrated on from device
Part structure and technological angle reduce peak value electric field to weaken the influence of inverse piezoelectric effect, such as oblique gate technique, field plate techniques.This is not
Technology difficulty and control difficulty are only increased, and certain influence is also produced on the frequency characteristic of device, the height of device is limited
Frequency is applied.
The content of the invention
Proposed by the present invention is a kind of highly reliable A lGaN/GaN heterostructure design methods, it is intended to deposited for prior art
Drawbacks described above, improved at all from design on material structure aspect, by setting up AlGaN/AlN/GaN HEMT hetero-junctions
Structure deformation relaxation model, and bring the model into conventional heterostructure band and the calculating of two-dimensional electron gas surface density, for
Specific two-dimensional electron gas surface density target design value, obtains optimal AlGaN potential barrier Al component x and AlN insert layer thickness
dAlNParameter so that AlGaN/AlN/GaN heterostructure barriers layer relaxivity reaches minimum, reduces under high field action by inverse piezoelectricity
Material stress caused by effect, suppresses defect and produces, so that the purpose for improving long term device reliability is reached, with high lattice matter
The advantages of amount, low-relaxivity and reduction research cost.
The technical solution of the present invention:A kind of design method of highly reliable A lGaN/GaN heterojunction structures, successively including such as
Lower step:
a)In substrate(1)On grow nucleating layer successively(2), cushion(3), channel layer(4), AlN insert layers(5), AlGaN
Barrier layer(6), two-dimensional electron gas is formed at AlN/GaN interfaces(7);
B) when AlN insert layers(5)Thickness dAlN=0, keep material other parameters constant, change AlGaN potential barrier(6)In
Al components x(0.1≤x≤0.4), grow a series of AlGaN/GaN heterogeneous structure materials, sample size >=3;Calculate AlGaN gesture
Barrier layer strains f=0.077x/3.189, statistics AlGaN potential barrier strain f and two-dimensional electron gas surface density measured result ns;
c)Based on conventional heterostructure band and two-dimensional electron gas surface density computational methods, sample is calculated, adjusted
AlGaN potential barrier(6)Relaxivity R make the two-dimensional electron gas surface density of calculating equal with measured result, obtain one group of AlGaN gesture
Barrier layer strains the data [f, R] of f and deformation relaxation degree R corresponding relations(8);Based on above-mentioned data [f, R](8), using function
Curve-fitting method, sets up using AlGaN potential barrier and strains f as independent variable, deformation relaxation degree RstressFor the relational model of dependent variable
Rstress(f)(9);
D) AlGaN potential barrier is worked as(6)Middle Al components x≤0.2, keeps material other parameters constant, changes AlN insert layers
(5)Thickness dAlN(0nm≤dAlN≤1nm), grow a series of AlGaN/AlN/GaN heterojunction structures, sample size >=3, statistics
AlN insert layers thickness, two-dimensional electron gas surface density measured result ns;
e)Based on conventional heterostructure band and two-dimensional electron gas surface density computational methods, sample is calculated, adjusted
AlxGa1-xThe relaxivity R of N barrier layers makes the two-dimensional electron gas surface density of calculating equal with measured result, obtains one group of AlN insertion
Layer thickness dAlNWith the data [d of AlGaN potential barrier relaxivity R' corresponding relationsAlN, R'](10);Based on above-mentioned data [dAlN,
R'](10), using function curve fitting process, set up with AlN insert layer thickness dsAlNFor independent variable, the relative relaxation of AlGaN potential barrier
Henan degree RrelativeFor the relational model R of dependent variablerelative(dAlN)(11);
f)When AlN insert layers(5)Thickness dAlN>When 0, AlGaN potential barrier is calculated(6)Strain, wherein x is AlGaN potential barrier Al components, RrelativeIt is the relative relaxivity of barrier layer;Due to
AlGaN potential barrier strain f is Al components x and relative relaxivity RrelativeFunction, and RrelativeFor AlN thickness dsAlNLetter
Number, so AlGaN potential barrier deformation relaxation degree RstressFor Al component x and AlN thickness dsAlNFunction, i.e. Rstress(f)= Rstress
(x,Rrelative)= Rstress(x, dAlN);
g)The total relaxivity R of AlGaN potential barriertotal=AlGaN potential barrier is with respect to relaxivity Rrelative(dAlN)+strain relaxes
Henan degree Rstress(x,dAlN), by the total relaxivity R of AlGaN potential barriertotalBring conventional heterostructure band and two-dimensional electron gas into
Among surface density is calculated, different Al components x and AlN thickness ds are calculatedAlNTwo-dimensional electron gas surface density curve, wherein abscissa is
AlN insert layer thickness dsAlN, ordinate is two-dimensional electron gas surface density ns, x is parameter;
h)Two-dimensional electron gas surface density target design value needed for being developed for device(12), select and the design load level
That tangent two-dimensional electron gas surface density of line with AlN insert layer thickness change curve(13), obtain curve(13)It is corresponding
AlGaN potential barrier Al components x0, and point of contact(14)Abscissa dAlN0, the as relaxation of most optimum materials parameter, now material structure
Henan degree is minimum.
Beneficial effects of the present invention:There is advantages below in terms of existing technologies:
1)Tradition improvement is caused by inverse piezoelectric effect mostly from device structure design and work the problem of device performance degeneration
Skill is improved and set out, and sizable process costs on the one hand can be spent to carry out process exploitation, on the other hand, due to the change of grid structure
Introducing with field plate techniques will increase the ghost effect of device, so as to limit the further lifting of device frequency performance;
2)In the case where AlGaN/GaN material structures and technique are constant, based on external devices structure and process modification come
The space of boost device reliability is limited;
3)The present invention is a kind of highly reliable A lGaN/GaN heterostructure design methods, can from material angle at all improve by
The integrity problem that inverse piezoelectric effect is brought, plays the performance of device to greatest extent;
4)Because the stress of AlGaN potential barrier is not only related to its thickness and Al components, also by the shadow of Material growth technique
Ring, and be difficult accurately to be tested by experimental method, thus it is also very big based on the relaxivity difficulty that experimental method reduces material,
And material and device technology development cost can be substantially reduced based on design method in the present invention, it is to avoid high-volume flow and test
The waste caused.
Brief description of the drawings
Fig. 1 is conventional AlGaN/AlN/GaN heterojunction structures schematic diagram;
Fig. 2 is relaxivity R in the present inventionstressF variation relation model schematic is strained with AlGaN potential barrier;
Fig. 3 is relaxivity R in the present inventionrelativeWith AlN insert layer thickness dsAlNVariation relation model schematic;
Fig. 4 is AlGaN/AlN/GaN heterojunction structure two-dimensional electron gas surface densities n in the present inventionsWith AlN insert layer thickness
dAlNWith Al components x variation relation schematic diagram.
1 in figure is substrate, and 2 be nucleating layer, and 3 be AlyGa1-yN cushions, and 4 be GaN channel layers, and 5 be AlN insert layers,
6 be barrier layer, and 7 be two-dimensional electron gas, and 8 be data [f, R], and 9 be model Rstress(f), 10 be data [dAlN, R'], 11 are
Model Rrelative(dAlN), 12 be two-dimensional electron gas target design value, and 13 are and the corresponding level of two-dimensional electron gas target design value 12
Line is tangentCurve, 14 be point of contact.
Embodiment
The present invention is further described below in conjunction with the accompanying drawings.
As shown in Fig. 1 ~ 4, a kind of design method of highly reliable A lGaN/GaN heterojunction structures, design procedure is included such as successively
Under:
a)In substrate(1)On grow nucleating layer successively(2), cushion(3), channel layer(4), AlN insert layers(5), AlGaN
Barrier layer(6), two-dimensional electron gas is formed at AlN/GaN interfaces(7);
B) when AlN insert layers(5)Thickness dAlN=0, keep material other parameters constant, change AlGaN potential barrier(6)In
Al components x(0.1≤x≤0.4), grow a series of AlGaN/GaN heterogeneous structure materials, sample size >=3;Calculate AlGaN gesture
Barrier layer strains f=0.077x/3.189, statistics AlGaN potential barrier strain f and two-dimensional electron gas surface density measured result ns;
c)Based on conventional heterostructure band and two-dimensional electron gas surface density computational methods, sample is calculated, adjusted
AlGaN potential barrier(6)Relaxivity R make the two-dimensional electron gas surface density of calculating equal with measured result, obtain one group of AlGaN gesture
Barrier layer strains the data [f, R] of f and deformation relaxation degree R corresponding relations(8);Based on above-mentioned data [f, R](8), using function
Curve-fitting method, sets up using AlGaN potential barrier and strains f as independent variable, deformation relaxation degree RstressFor the relational model of dependent variable
Rstress(f)(9);
D) AlGaN potential barrier is worked as(6)Middle Al components x≤0.2, keeps material other parameters constant, changes AlN insert layers
(5)Thickness dAlN(0nm≤dAlN≤1nm), grow a series of AlGaN/AlN/GaN heterojunction structures, sample size >=3, statistics
AlN insert layers thickness, two-dimensional electron gas surface density measured result ns;
e)Based on conventional heterostructure band and two-dimensional electron gas surface density computational methods, sample is calculated, adjusted
AlxGa1-xThe relaxivity R of N barrier layers makes the two-dimensional electron gas surface density of calculating equal with measured result, obtains one group of AlN insertion
Layer thickness dAlNWith the data [d of AlGaN potential barrier relaxivity R' corresponding relationsAlN, R'](10);Based on above-mentioned data [dAlN,
R'](10), using function curve fitting process, set up with AlN insert layer thickness dsAlNFor independent variable, the relative relaxation of AlGaN potential barrier
Henan degree RrelativeFor the relational model R of dependent variablerelative(dAlN)(11);
f)When AlN insert layers(5)Thickness dAlN>When 0, AlGaN potential barrier is calculated(6)Strain, wherein x is AlGaN potential barrier Al components, RrelativeIt is the relative relaxivity of barrier layer;Due to
AlGaN potential barrier strain f is Al components x and relative relaxivity RrelativeFunction, and RrelativeFor AlN thickness dsAlNLetter
Number, so AlGaN potential barrier deformation relaxation degree RstressFor Al component x and AlN thickness dsAlNFunction, i.e. Rstress(f)= Rstress
(x,Rrelative)= Rstress(x, dAlN);
g)The total relaxivity R of AlGaN potential barriertotal=AlGaN potential barrier is with respect to relaxivity Rrelative(dAlN)+strain relaxes
Henan degree Rstress(x,dAlN), by the total relaxivity R of AlGaN potential barriertotalBring conventional heterostructure band and two-dimensional electron gas into
Among surface density is calculated, different Al components x and AlN thickness ds are calculatedAlNTwo-dimensional electron gas surface density curve, wherein abscissa is
AlN insert layer thickness dsAlN, ordinate is two-dimensional electron gas surface density ns, x is parameter;
h)Two-dimensional electron gas surface density target design value needed for being developed for device(12), select and the design load level
That tangent two-dimensional electron gas surface density of line with AlN insert layer thickness change curve(13), obtain curve(13)It is corresponding
AlGaN potential barrier Al components x0, and point of contact(14)Abscissa dAlN0, the as relaxation of most optimum materials parameter, now material structure
Henan degree is minimum.
The barrier layer(6)Thickness dAlGaNFor 5nm≤dAlGaN≤30nm。
The AlyGa1-yN cushions(3)In Al components y be 0≤y≤0.08, thickness is。
The substrate(1)Including SiC, sapphire, Si or GaN.
The conventional heterostructure band and two-dimensional electron gas surface density computational methods include self-consistent solution Schrodinger equation and
Poisson's equation and the method for only solving Poisson's equation.
The curve-fitting method of the use, fitting function for linear, multinomial, index or logarithmic form one kind or
It is several.
Embodiment:
A) growing AIN nucleating layer 2,1 μm of GaN cushions 3,200nmGaN channel layers 4, AlN successively in SiC substrate 1
Insert layer 5, the thick AlGaN potential barriers 6 of the 20nm that undopes, constitute GaN HEMT heterojunction structures, heterogeneous interface formation two-dimensional electron gas
7;
B) keep material other parameters constant, if AlN insert layer thickness dsAlN=0, change the Al components in AlGaN potential barrier
X is 0.1,0.15,0.2,0.25,0.3, and calculating the strain in AlGaN using f=0.077x/3.189 obtains f1、f2、f3、f4、
f5, measure its two-dimensional electron gas surface density n1、n2、n3、n4、n5;
C) using the method for conventional self-consistent solution Schrodinger equation and Poisson's equation, with the relaxivity in AlGaN potential barrier 6
R is adjustable parameter so that result of calculation is identical with experimental result, obtains R1、R2、R 3、R 4、R 5, using formula
Above-mentioned data [f, R] 8 are fitted, and obtain straining f as independent variable, deformation relaxation degree using AlGaN potential barrier
RstressFor the functional relation R of dependent variablestress(f) 9, wherein parameter A=500, B=8000, C=1.25 × 10-4, such as Fig. 2 institutes
Show;
D) Al components x is 0.2 in fixed AlGaN potential barrier, while material other parameters are constant, changes AlN insertion thickness
Spend for 0.2,0.4,0.6,0.8,1.0, measure its two-dimensional electron gas surface density、、、、;
E) using the method for conventional self-consistent solution Schrodinger equation and Poisson's equation, with the relaxation in AlGaN potential barrier 6
Degree R is adjustable parameter so that result of calculation is identical with experimental result, obtains、、、、, using formula
AlN insert layer thickness dsAlNWith the data [d of AlGaN potential barrier relaxivity R' corresponding relationsAlN, R'] 10 intended
Close, obtain with AlN insert layer thickness dsAlNIt is independent variable, the relative relaxivity R of AlGaN potential barrierrelativeFor the function of dependent variable
Rrelative(dAlN) 11, wherein parameter xsub=0.15, x=0.2 are the Al components in AlGaN potential barrier 6, as shown in Figure 3;
f)When AlN insert layers(5)Thickness dAlN>When 0, AlGaN potential barrier(6)Strain be, wherein x is AlGaN potential barrier Al components;
G) the total relaxivity R of AlGaN potential barriertotal=Rrelative+Rstress, it is updated to self-consistent solution Schrodinger equation
In Poisson's equation, calculate two-dimensional electron gas surface density and closed with the change of Al components in AlN insert layers thickness and AlGaN potential barrier
System, as shown in Figure 4;
H) two-dimensional electron gas surface density target design value 12 needed for device is developed is set as 9.8 × 1012cm-2, then choose and mesh
Mark tangent that root two-dimensional electron gas surface density n of the corresponding horizontal line of design load 12sWith AlN insert layer thickness dsAlNChange curve
13, obtain Al components x in the corresponding AlGaN potential barrier of curve 130=0.25, and point of contact 14 abscissa, i.e. AlN insertion
Layer thickness dAlN0=0.51, now barrier layer relaxivity is minimum, reliability of material highest;
Described above is only the preferred embodiment of the present invention, it should be pointed out that:For the ordinary skill people of the art
For member, under the premise without departing from the principles of the invention, some improvements and modifications can also be made, these improvements and modifications also should
It is considered as protection scope of the present invention.