JPH08136485A - Heterostructure evaluating method - Google Patents

Abstract

PURPOSE: To evaluate structural fluctuation with high resolution as precise as nano meter scale by detecting the difference of interference conditions of electron waves in heterostructures based on the fluctuation of the current values at the time when voltage is swept and applied. CONSTITUTION: Regarding a resonance tunnel structure consisting of a base structure composed of AlAs barrier layers 1, 2 with the thickness of 11 molecular layers (LM) and an InGaAs well layer 3 with the thickness of 18LM, electrode layers 4, 5. and electrodes 6, 7; voltage is so applied to the electrodes 6, 7 as to cross the structure transversely. Then, the dependence of the ratio of the current I to the current Io in the base structure on the applied voltage Vs is measured; said current I is the current at the time when the thickness of the layers 1, 2 or the layer 3 is fluctuated by 1ML increase or decrease. Consequently, the difference of interference conditions of electron waves reflecting the structural fluctuation is detected as the alteration of current values and the structural fluctuation in each layer 1, 2, 3 can be evaluated. At that time, since the spread of the electron waves is de Broglie's wavelength (several 10nm), evaluation with resolution as precise as nano meter scale can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron / optical device having a heterostructure, in which current-voltage characteristics are measured and film thickness fluctuations, potential fluctuations, potential distribution fluctuations and single crystallinity which affect the device characteristics are measured. The present invention relates to a heterostructure evaluation method for evaluating fluctuations (hereinafter collectively referred to as structural fluctuations).

[0002]

2. Description of the Related Art Various structures using a heterostructure have been proposed in order to improve the performance of a device, but the structural fluctuation in the heterostructure has a great influence on the performance of the device. In particular, in the device structure using the quantum effect to increase the operating speed of the device, since the size (layer thickness) of the heterostructure is equal to the electron wavelength, the device characteristics are very sensitive to structural fluctuations. Structural fluctuations on the nanometer scale are said to significantly degrade the device performance.

[0003]

Therefore, it is indispensable to establish a technique for forming an element structure having no structural fluctuation, and for that purpose, a technique for evaluating the structural fluctuation with high accuracy is required. For the interface analysis method of the hetero structure, the surface shape after forming each thin film forming the hetero structure is evaluated by using a scanning tunneling microscope (STM) or an atomic force microscope (AFM), and each interface structure of the hetero structure is evaluated. There is a method of indirectly predicting. However, this method has a problem in that the interface structure after the device is manufactured cannot be precisely determined.

On the other hand, as a method of analyzing the interface formed under the surface, photoluminescence (PL), cathodoluminescence (CL), and photoluminescence excitation (PL) are used.
E) and the like have been used. All of these methods utilize the luminescence and absorption of excitons bound in the quantum well structure sandwiched between the barrier layers, so that among the layers forming the structure, fluctuations in the structure of the quantum well layer are Although applicable to evaluation, it is not possible to evaluate structural fluctuation of all layers including other barrier layers. In addition, the resolution is determined by the size of the input / output probe and the diffusion effect during exciton measurement, and the value remains on the sub-μm scale.

Further, as a technique for evaluating the interface formed under the surface, there is a ballistic electron emission microscope (BEEM) applying the STM technique, and the structural fluctuation of the Schottky junction interface can be measured with a resolution of nanometer scale. However, in this BEEM, a part (10% or less) of the tunnel current used to determine the distance between the probe and the sample is used as a signal for interface evaluation, so the current that can be passed through the structure is limited to a minute value. ing. Therefore, the structure to which BEEM can be applied is limited to a simple structure such as a single junction, and it is often difficult to apply it to the evaluation of a hetero structure formed of a multilayer thin film.

The present invention has been made to solve the above problems, and enables structural fluctuations in a heterostructure to be evaluated with high precision and resolution on the nanometer scale. The purpose is to

[0007]

According to the method for evaluating a heterostructure of the present invention, a voltage is applied across a heterostructure in a voltage range in which a current flowing due to wave properties is dominant, and the applied voltage is applied. The change in the current value when the value is changed is measured, and the change in the structure of each layer constituting the hetero structure is determined by the change in the current value in the voltage range including before and after the current value reaches the maximum value. Characterized by evaluation. Further, the heterostructure evaluation method of the present invention, in the voltage range in which the current flowing due to the wave nature is dominant, applies a voltage across the heterostructure to be measured, and changes the applied voltage value. By measuring the change in the current value when the current value changes, and comparing the change in the current value in the voltage range including before and after the maximum current value with the maximum value, by comparing with the change in the current value by the reference heterostructure, It is characterized in that changes from the heterostructure, which is a structural reference of each layer constituting the heterostructure, are evaluated. Then, the heterostructure evaluation method of the present invention applies a voltage across the structure in the first region of the heterostructure to be measured in the voltage range in which the current flowing due to the wave nature is dominant, and applies this. The first change, which is the change in the current value when the voltage value is changed, is measured, and the structure is measured in the second region of the heterostructure to be measured in the voltage range in which the current flowing due to the wave nature is dominant. A voltage is applied so as to traverse, and the second change, which is the change in the current value when the applied voltage value is changed, is measured, and before and after the maximum changes in the first and second changes, respectively. It is characterized in that the distribution of the structural change of each layer forming the heterostructure is evaluated by comparing the changes in the current value in the voltage range including

[0008]

According to the structural fluctuation of the heterostructure, there is a difference in the interference condition of the electron wave in the heterostructure, which is detected by the change of the current value when the voltage is swept and applied.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, the outline of the present invention will be described below. This invention utilizes the wave nature of electrons. At each location in the heterostructure, due to the structural fluctuation, the interference condition of the electron wave differs depending on the structural fluctuation. The structure fluctuation is evaluated by detecting the difference in the interference condition. Specifically, a current including at least one voltage V _p that maximizes the probability of electron transmission, which is the voltage dependence of the current applied to the hetero structure by the electrons passing through the hetero structure due to its wave nature −
With a heterostructure exhibiting voltage characteristics, the current is measured at an applied voltage V _s in the range of 0 ≦ V _s ≦ V ₀ (where V _p ≦ V ₀ ), and compared with the results measured at different locations.

At the same applied voltage, it is mainly the transmission probability that the influence of structural fluctuations on the current is included in the amount that contributes to the current, and the value of the transmission probability changes greatly especially near the maximum value. have. From this, if a current ratio is adopted as a comparison method, for example, the effect of structural fluctuation, that is, the difference in electron transmission probability depending on the difference in interference conditions is mainly reflected. Also, when applying an atomic force microscope or the like to the evaluation as a measurement method in a minute region, taking the ratio of the currents has an influence other than the heterostructure,
For example, there is an advantage that effects such as contact resistance can be offset.

As described above, from the ratio of the currents, it is possible to analyze the structural fluctuation between the thin films forming the heterostructure and the size thereof at different measured locations. Since the spread of the electron wave is about the de Broglie wavelength (tens of nm), the present invention enables analysis with a resolution on the nanometer scale.

An embodiment of the present invention will be described below with reference to the drawings. Example 1. In this embodiment, the two barrier layers 1 and 2 made of AlAs and the well layer 3 made of InGaAs shown in FIG.
In the resonance tunnel structure (RTD structure) composed of and, the fluctuation of the width of the barrier layers 1 and 2 is ± 1 molecular layer (hereinafter,
The present invention was applied to the evaluation of single structure fluctuations existing separately (referred to as 1ML). In addition, 4, 5 are electrode layers and 6, 7
Is an electrode. First, the current-voltage characteristics (hereinafter referred to as IV characteristics) of the RTD structure will be described.

When electrons are incident on the RTD structure from the current layer 4, the transmission probability of electrons that are transmitted (tunneled) by the tunnel effect due to the reflection of the wave function in the barrier layer 1 is close to 0 in most cases. However, when a specific electron wave interference condition (hereinafter referred to as resonance condition) is satisfied, that is, a path difference corresponding to a phase difference determined by the layer thicknesses of the barrier layers 1 and 2 and the well layer 3 is the de Broglie wavelength of the incident electron. In the case of half the value of, the reflected electron wave by the RTD structure is canceled,
The electron transmission probability approaches 1. In particular, there is a resonance condition in which the transmission probability is 1 when the applied voltage to the RTD structure is 0.

When the applied voltage is V _s (> 0 V), the electron velocity emitted from the RTD structure and the RTD
It is known that there is always an electron reflected from the entire RTD structure because the velocity of the electrons incident on the structure is different, so that the transmission probability thereof is a value slightly less than 1. In addition, in an RTD structure composed of a barrier layer and a well layer having a certain fixed structure, whether or not to resonate depends on the wavelength of the incident electron, and the incident electron has the R
If the wavelength satisfies the condition of resonance in the TD structure, the tunnel transmission probability approaches 1, and if the applied voltage is 0, it becomes 1.

That is, when the electron has energy having a wavelength satisfying the resonance condition, the electron tunnels through the RTD structure by a characteristic tunnel effect (resonant tunnel effect) satisfying the resonance condition. In such a resonant tunnel effect, the tunnel transparency determined by the interference effect due to the multiple reflection of the electron wave is similar to the selective transparency of the wavelength by the resonator in optics. It is noticeable. Therefore, at the applied voltage V _s = V _p that gives the resonance condition, the tunnel penetration probability of electrons rapidly approaches 1, and if the resonance condition is deviated even slightly, the tunnel penetration probability rapidly approaches 0.

Therefore, the current I ₀ flowing through the RTD structure has the maximum value when the applied voltage Vs = Vp and exhibits the IV characteristic as shown in FIG. As described above, changing the voltage applied to the RTD structure changes the energy giving the maximum value of the energy distribution of the incident electrons, that is, changing the wavelength giving the maximum value of the wavelength distribution of the incident electrons. Therefore, if the applied voltage is changed, the point that becomes the resonance condition appears in the change in the measured current value.

[0017] FIG. 3 is a cross-sectional view of a device having a RTD structure, the barrier layer of 1 thick L _b1 = 11 mL made of AlAs (molecular layer), 2 a thickness L _b2 = 11M made of AlAs
L barrier layer, 3 is InG with an indium composition ratio of 0.2
Well layers made of aAs and having a thickness L _w = 18 ML, 4 and 5 are electrode layers made of GaAs into which n-type impurities are introduced,
Reference numerals 6 and 7 denote electrodes having an RTD structure having the barrier layers 1 and 2 and the well layer 3 as a reference structure. Reference numerals 8 and 9 are spacers made of GaAs having a thickness of 5 ML for preventing the n-type impurities from diffusing from the electrode layers 4 and 5 from entering the RTD structure.

From this reference structure, the ratio of the current I when the thickness of the barrier layers 1 and 2 or the well layer 3 is increased or decreased by 1 ML to the current I ₀ in the reference structure depends on the applied voltage Vs (hereinafter, I
/ I ₀ -V characteristic) is shown in FIGS.
FIG. 4 shows the calculation result of the I / I ₀ -V characteristic when the thickness of the barrier layer 1 on the high energy side is increased or decreased by 1 ML, 41 shows the calculation result when the thickness is increased by 1 ML, and 42 is decreased by 1 ML. The calculation result in the case is shown.

FIG. 5 shows the barrier layer 2 on the low energy side.
Shows the calculation result of the I / I ₀ -V characteristic when the thickness of 1 is increased / decreased by 1 ML, 51 shows the calculation result when the thickness is increased by 1 ML, and 52 shows the calculation result when the thickness is decreased by 1 ML. FIG. 6 shows I when the thickness of the well layer 3 is increased or decreased by 1 ML.
The calculation result of the / I ₀ -V characteristic is shown, 61 shows the calculation result in the case of 1 ML increase, and 62 shows the calculation result in the case of 1 ML decrease.

As can be seen from these FIGS. 4 to 6, it can be seen that the I / I ₀ -V characteristic mainly changes at V _p / 2. In the applied voltage range of V _s <V _p / 2, the influence of fluctuations in the thickness of the barrier layers 1 and 2 mainly appears. For example, when the barrier layers 1 and 2 are thinned by 1 ML, as shown in FIGS.
In this range, the value of I / I ₀ is approximately tripled. On the other hand, even if the thickness of the well layer 3 is increased or decreased by 1 ML, as shown in FIG. 6, the value of I / I ₀ is about 1 in this range and I is I _0.
It is a value that does not change.

In the above-mentioned range, these are because the resonance tunnel effect does not occur because the energy difference between the Fermi level and the resonance level is large, and the electrons behave as if they tunnel through a single barrier.

On the other hand, in the applied voltage range of V _p / 2 <V _s <V _p , the influence of the fluctuation of the thickness of the well layer 3 becomes prominent. For example, when the well layer 3 becomes 1 ML thick, as shown in FIG. 6, the value of I / I ₀ becomes 100 times in this range. In the applied voltage range of V _p / 2 <V _s <V _p ,
The applied voltage dependency of I / I ₀ differs depending on which of the two barrier layers 1 and 2 has a fluctuation in layer thickness.

This is because the state of electron distribution on the high energy side of each barrier is different near the resonance condition. In the applied voltage range described above, electrons are distributed on the high energy side of the barrier layer 1 according to the Fermi distribution, and particularly in the vicinity of the Fermi level, the electron distribution function changes from 1 to 0 as the electron energy increases. Therefore, when there is almost no difference in energy between the Fermi level and the resonance level, the number of electrons tunneling through the barrier layer 1 to reach the resonance level includes the electrons near the Fermi level on the high energy side of the barrier layer 1. The influence of distribution change appears strongly.
Therefore, the effect of changing the transmission probability due to the increase / decrease of the barrier layer 1 by about 1 ML is buried in the effect and is difficult to appear. Therefore, in the vicinity of V _p , the value of I / I ₀ approaches 1, and the effect of the layer width fluctuation of the barrier layer 1 is virtually undetectable.

On the other hand, in the above-mentioned applied voltage range, there is a resonance level on the high energy side of the barrier layer 2, and this level has a very narrow level width. Therefore, when the electrons in the resonance level tunnel through the barrier layer 2, the number of electrons is almost unaffected by the change in the electron distribution in the vicinity of the resonance level. The effect of appears strongly. As a result, even when there is almost no energy difference between the Fermi level and the resonance level, that is, even near V _p , 0
As in the case of <V _s <V _p / 2, the influence of the fluctuation of the layer width of the barrier layer 2 is detected. From FIGS. 4 to 6, the I / I ₀ -V characteristics are complicated when the voltage exceeds −V _p .

The changes in I / I ₀ values shown in FIGS. 4 to 6 due to single structure fluctuations in the RTD structure are summarized in Table 1 below.

[0026]

From Table 1, it can be seen that: First, when 0 <V _s <V _p / 2, there is fluctuation of the barrier layer thickness /
I know nothing. Further, when V _p / 2 <V _s <V _p , it can be seen that the fluctuation of the well layer thickness is present or absent. And 0 <V _s <V
It is possible to detect which of the two barrier layers the barrier layer whose fluctuation is found at _p / 2 is. Therefore, by comparing the current I _{0 of the} reference structure with the current I of the structure to be evaluated, for each of the three layers forming the RTD structure, the layer number fluctuation distribution from the reference structure is calculated in 1 ML units. It can be separated and determined separately.

Embodiment 2 FIG. In the second embodiment, in the RTD structure composed of the two barrier layers 1 and 2 and the well layer 3 shown in FIG. 3, the fluctuation of the width of the barrier layers 1 and 2 and the fluctuation of the width of the well layer 3 exist at the same time. The case will be described. FIG.
FIG. 7 shows the calculation results of the I / I ₀ -V characteristics when the thickness of the well layer 3 is increased by 1 ML and the barrier layer 1 or the barrier layer 2 is decreased by 1 ML from the reference structure shown in FIG.

From FIG. 7, mainly at V _p / 2 as a boundary, I
It can be seen that the / I ₀ -V characteristic changes. 0 <V _s <V
_In the range of the applied voltage of _p / 2, the influence of the fluctuation of the barrier layer thickness mainly appears. For example, if the barrier layer 1 becomes 1 ML thinner,
The value of I / I ₀ is approximately tripled. On the other hand, even if the thickness of the well layer 3 is increased by 1 ML, the value of I / I ₀ is almost 1 and I is I _0.
It is a value that does not change. Because the energy difference between the Fermi level and the resonance level is large, the resonance tunnel effect does not occur, and the electron behaves as if it were tunneling through a single barrier.

On the other hand, in the applied voltage range of V _p / 2 <V _s <V _p , the influence of the fluctuation of the thickness of the well layer 3 appears. For example, when the well layer 3 becomes 1 ML thick, the value of I / I ₀ becomes about 100 times. Further, in the applied voltage range of V _p / 2 <V _s <V _p , the value of I / I ₀ is applied depending on the fluctuation of the thickness of the barrier layers 1 and 2 added to the well layer 3. The voltage dependence is different. This is because the electron distribution on the high energy side of each barrier is different under the resonance condition.

Electrons are distributed according to the Fermi distribution on the high energy side of the barrier layer 1, and particularly near the Fermi level,
The distribution function of the electrons changes from 1 to 0 as the energy of the electrons increases. Therefore, when there is almost no difference in energy between the Fermi level and the resonance level, the number of electrons tunneling through the barrier layer 1 to reach the resonance level includes the electrons near the Fermi level on the high energy side of the barrier layer 1. The influence of distribution change appears strongly. Therefore, the effect of changing the transmission probability due to the increase / decrease of the barrier layer 1 by about 1 ML is buried in the effect and becomes difficult to appear. Therefore, in the vicinity of V _p , the value of I / I ₀ is well layer 3
1 approaches the value in the case of only the fluctuation of 1 ML, and apparently the influence of the fluctuation of the width of the barrier layer 1 is not detected.

On the other hand, in the above-mentioned applied voltage range, there is a resonance level on the high energy side of the barrier layer 2, and this level has a very narrow level width. Therefore, the number of electrons when electrons at the resonance level tunnel through the barrier layer 2 is hardly affected by the change in the electron distribution near the resonance level. Therefore, the effect of changing the transmission probability by the increase or decrease of the barrier layer 2 by about 1 ML is strongly exhibited. As a result, when there is almost no difference in the energy levels of the resonance levels, that is, even near V _p , 0 <V
s <As in the case of Vp / 2, the remaining effects of layer width fluctuations of the barrier layer 2, which is the value of I / I ₀ due to the influence of the value thickness fluctuation of the well layer 3 of I / I _0, It appears as a result that the value becomes close to the product of I / I ₀ values due to the influence of the thickness fluctuation of the barrier layer 2.

Table 2 summarizes the change in the current value ratio shown in FIG. 7 due to the composite structure fluctuation of the RTD structure in the second embodiment.

[0034]

From Table 2, it can be seen that: First, when 0 <V _s <V _p / 2, there is fluctuation of the barrier layer thickness /
I know nothing. Further, when V _p / 2 <V _s <V _p , 0 <V
It is possible to detect which of the two barrier layers the barrier layer of which the fluctuation is found when _s <V _p / 2. Therefore, by comparing the current I _{0 of the} reference structure with the current I of the structure to be evaluated, the structure fluctuation from the reference structure when the composite structure fluctuation of the layers forming the RTD structure is 1ML.
Each unit can be separated and distinguished separately.

In the above embodiment, the present invention is applied to the RTD.
Although the example applied to the structure has been described, the present invention is not limited to this. The present invention is also applicable to any heterostructure in which the current density of electrons passing through the heterostructure (current density due to carriers) due to the wave nature can measure the applied voltage dependency to the heterostructure. For example, it can be applied to the evaluation of the structural fluctuation of a single heterojunction, a single barrier structure, a multiple coupled quantum well structure, and a multiple tunnel barrier structure.

Example 3. The third embodiment of the present invention will be described below. In Example 3, the IV characteristic measurement of the micro region of the RTD structure is performed using the IV measurement method having a high spatial resolution, and the in-plane distribution of the element structure fluctuation of the RTD structure in the nano region of the micro region is measured. An example of measurement of Here, the RTD structure was evaluated using a measurement system to which an atomic force microscope was applied as shown in FIG.

FIG. 8 is a configuration diagram showing the configuration of a measurement system to which the atomic force microscope is applied. In FIG.
Is an RTD including the barrier layers 1 and 2 and the well layer 3 shown in FIG.
Structure, 10 is a conductive probe capable of scanning in two dimensions, 11
Is a voltage source, 12 is an ammeter for measuring the value of current flowing through the conductive probe 10, and other reference numerals are the same as in FIG. Then, according to the current value measured by the ammeter 12, FIG.
An image of the current distribution is obtained as shown in.

Since the value of the current flowing through the RTD structure 1a is proportional to the contact area of the conductive probe 10, the tip of the conductive probe 10 has a diameter of, for example, 20 nm or less.
It is possible to measure the IV characteristic of a minute area on the nanometer scale. For example, after excessively applying a voltage to destroy the part of the element under the conductive probe 10 of the element, a normal RTD IV characteristic can be measured at a position laterally moved from that position by 10 to 20 nm. . From this, 10-20
It can be seen that the current distribution can be measured with an in-plane resolution of nm.

As the RTD structure 1a of this embodiment, I
A thickness of 18M made of InGaAs with a composition ratio of n of 0.2
A well layer of L (about 5.4 nm) and a barrier layer of 11 ML (about 3.1 nm) made of AlAs sandwiching the well layer were used. Further, the applied voltage V _s = 0.
It was conducted under the condition of 8V. This applied voltage is the RTD in the device.
It is a voltage for applying a voltage included in the range of V _p / 2 <V _s <V _{p to} the structure 1a.

FIG. 9 shows a current image obtained as a result of performing this measurement in a region of 200 nm × 200 nm. In FIG. 9, the large detected current value I is shown in white. That is, the current image is divided into two parts, a dark part showing the current value I ₀ and a bright part showing the current value I. In this embodiment, the ratio I / I ₀ between them is 1 when the current value in the dark part is 1. 1
It is 00 or more.

The current ratio in the bright part and the dark part of the current image shown in FIG. 9 is different by 100 times or more, and comparing this result with the calculation result in Table 1, this corresponds to the difference of 1 ML in the well layer. From this, it is shown in this current image that there is a 1 ML fluctuation distribution in the well layer thickness. This measurement result is
By applying the present invention to a nanometer-scale IV characteristic measuring device (measuring system to which an atomic force microscope is applied), 10 nm to 2 nm within 200 nm × 200 nm is obtained.
It shows that the in-plane distribution of the layer number (layer thickness) fluctuation of 1 ML could be measured with the in-plane resolution of 0 nm.

By the way, in Example 3, since the tip of the conductive probe 10 has a diameter of about 20 nm, Al
The in-plane distribution of the fluctuation of the number of layers of the barrier layer made of As cannot be measured. This is because in the case of AlAs, the fluctuation of about one molecular layer exists in the size of the region of about 5 nm × 5 nm, and this size is much smaller than the tip diameter of the conductive probe 10. In the case of InGaAs forming the well layer in this embodiment, the fluctuation of about the molecular layer thereof mainly changes depending on the size of the region having a size of about 100 nm × 100 nm, so that the tip has a diameter of about 20 nm. With the sex probe 10, the in-plane distribution of the fluctuation of the number of layers can be measured.

As described above, by using the present invention, it is possible to measure the in-plane distribution of the structural fluctuation of the heterostructure with a resolution of nanometer scale. In addition, in the above-mentioned embodiment, the analysis of the structural fluctuation in one element having a heterostructure has been described, but the present invention is not limited to this.
It goes without saying that the present invention can also be applied to evaluation of structural fluctuations among a plurality of elements having a heterostructure. Further, in the above embodiment, the heterostructure composed of the semiconductor thin film is described, but the present invention is not limited to this, and the present invention can also be applied to the evaluation of the structural fluctuation of the heterostructure including the thin films of the metal and the insulator. .

[0045]

As described above, according to the present invention, the voltage applied to the heterostructure is swept, the change in the current value at that time is measured, and the heterostructure is evaluated by the change in the current value. I did it. By changing the voltage applied to the heterostructure, the energy that gives the maximum value of the energy distribution of the incident carriers is changed, and if the applied voltage is changed, the point that becomes the resonance condition is the measured current value. It will appear in the changes. Due to the difference in the change of the current value, one molecule layer or one layer of each layer forming the heterostructure is formed.
It is possible to detect structural fluctuations that are equivalent to fluctuations in the atomic layer thickness. Therefore, there is an effect that the structural fluctuation in the heterostructure can be evaluated with high accuracy and resolution on the nanometer scale.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a general configuration of a resonance tunnel structure.

FIG. 2 is a characteristic diagram showing a relationship between an applied voltage and a current to a resonance tunnel structure showing a resonance tunnel effect.

FIG. 3 is a cross-sectional view showing a configuration of a resonance tunnel structure to be measured in one example of the present invention.

FIG. 4 is an applied voltage V of the ratio of the current I and the current I ₀ in the reference structure when the thickness of the barrier layer 1 in FIG. 3 increases or decreases by 1 ML.
It is a characteristic diagram which shows the calculation result of s dependence.

5 is an applied voltage V of the ratio of the current I and the current I ₀ in the reference structure when the thickness of the barrier layer 2 in FIG. 3 is increased or decreased by 1 ML.
It is a characteristic diagram which shows the calculation result of s dependence.

6 is an applied voltage V of the ratio of the current I and the current I ₀ in the reference structure when the thickness of the well layer 3 in FIG. 3 increases or decreases by 1 ML.
It is a characteristic diagram which shows the calculation result of s dependence.

FIG. 7 shows an I / I ₀ − when the barrier layer 1 or the barrier layer 2 is increased by 1 ML in addition to the 1 ML increase of the well layer 3 of FIG.
It is a characteristic view which shows the calculation result of V characteristic.

FIG. 8 is a configuration diagram showing a configuration of a measurement system to which an atomic force microscope according to a third embodiment of the present invention is applied.

FIG. 9 shows the measurement in Example 3 of 200 nm × 200.
It is a characteristic view which shows the current distribution image which shows the result obtained by performing in the area | region of nm.

[Explanation of symbols]

1, 2 ... Barrier layer, 3 ... Well layer, 4, 5 ... Electrode layer, 6, 7
…electrode. 8, 9 ... Spacer, 10 ... Conductive probe, 11 ...
Voltage source, 12 ... Ammeter.

Claims (3)

[Claims] 1. A heterostructure evaluation method for a heterostructure composed of a plurality of thin films, wherein a voltage is applied across the heterostructure in a voltage range in which a current flowing due to wave properties is dominant, The change in the current value when the voltage value to be applied is changed is measured, and the change in the current value in the voltage range including before and after the current value reaches the maximum value indicates the change in the layers of the heterostructure. A heterostructure evaluation method, characterized by evaluating structural changes. 2. A heterostructure evaluation method for a heterostructure composed of a plurality of thin films, wherein a voltage is applied across a heterostructure to be measured in a voltage range in which a current flowing due to wave properties is dominant. Then, the change in the current value when the applied voltage value is changed is measured, and the change in the current value in the voltage range including before and after the current value reaches the maximum value is determined by the reference heterostructure. A heterostructure evaluation method, characterized in that a change from the reference heterostructure in the structure of each layer constituting the heterostructure is evaluated by comparing with a change in current value. 3. A heterostructure evaluation method for a heterostructure composed of a plurality of thin films, wherein the structure is traversed by a first region of the heterostructure to be measured in a voltage range in which a current flowing due to wave characteristics is dominant. Voltage is applied and the first change, which is the change in current value when the applied voltage value is changed, is measured, and the heterogeneity of the measurement target is measured in the voltage range in which the current flowing due to wave nature is dominant. A voltage is applied across the structure in the second region of the structure, and a second change, which is a change in the current value when the value of the applied voltage is changed, is measured. Among the changes, by comparing the degree of change of the current value in the voltage range including before and after the maximum, respectively, to evaluate the distribution of structural changes of each layer constituting the heterostructure, You Heterostructure evaluation method.