JPS5824952B2 - Gankou Kasoshi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Gunn effect element useful for improving the oscillation characteristics, particularly the frequency characteristics, of a solid-state oscillator.

Gunn effect elements for solid-state oscillators generally have an electron concentration distribution in the thickness direction as shown in Figure 1X, and have a high electron concentration (N
It has a low electron concentration active layer 2, such as an N-type GaAs layer, epitaxially grown on a + type) substrate 1, and a high electron concentration layer (electrode layer) 3 thereon for obtaining ohmic contact. The substrate 1 side is used as an anode, and the electrode layer 3 side is used as a cathode, and the normal operation layer 2 has a region 4 where the electron concentration distribution is almost flat in the thickness direction and an electron concentration transition region 5 where the electron concentration distribution changes in the thickness direction. have.

The electron concentration transition region 5 is a region from a portion where the electron concentration starts to increase to a portion where the electron concentration is four times that of the region 4, that is, a portion where the Habo domain disappears, and its thickness is as follows.
This is called the electron concentration transition width.

The existence of this electron concentration transition region 5 causes a decrease in gain and an increase in series resistance, resulting in a decrease in output. It is said to be about %.

In particular, in Gunn effect devices for millimeter wave bands (30 GHz or higher) where the active layer thickness is extremely small, the electron concentration transition width cannot be reduced by vapor phase epitaxial growth due to autodoping from the substrate. It was believed that the electron concentration transition width was negligible and narrow.

However, especially in the millimeter wave band, it is difficult to make the impedance of the load circuit sufficiently low from the viewpoint of machining accuracy, and even if the Gunn effect element described above is used, it is not only difficult to obtain the desired oscillation output, but also It was found that only inferior band characteristics and frequency characteristics were obtained.

An object of the present invention is to provide a Gunn effect element that can constitute a solid-state oscillator with significantly improved band characteristics and frequency characteristics without substantially reducing the oscillation output.

The Gunn effect element of the present invention is characterized in that, in the active crystal layer, the electron concentration transition width on the side that is in contact with the high electron concentration substrate occupies 40% to 100% of the width of the active crystal layer. This will be explained in detail.

FIG. 2 shows the electron concentration distribution of the Gunn effect element according to the example of the present invention.

This Gunn effect element is made of GaAs on an N++GaAs substrate 1.
The active layer 2 and the N+ type electrode layer 3 are formed by vapor phase epitaxial growth of s crystal, and the thickness of the active layer 2 is 1.58 m1, and the thickness of the electron concentration transition region 5, that is, the electron concentration transition width is The electron concentration NO in the 0.9 μm region 4 is 1×16 cE3.

Figure 3 shows the frequency characteristics obtained by mounting this Gunn effect element in an oscillation circuit, changing the oscillation frequency by changing the distance between the element and the variable shorting plate, that is, the short length, and measuring the oscillation output at that time. .

Curves 6, 7, and 8.9 in FIG. 3 are frequency characteristics when the susceptance of the oscillation circuit is changed, respectively.

For comparison, a Gunn effect element similar to that of the above example was fabricated, except that the electron concentration transition width was set to 0.3 μm, and the device was mounted in a similar oscillation circuit and its frequency characteristics were measured.

The results are shown in FIG. Curve 6' in FIG.
7', 8', and 9' are the curves 6, 7°, and 8. in Fig. 3, respectively.
This is the same oscillation circuit as No. 9, and the frequency characteristics are shown when the susceptance is changed.

As is clear from the comparison of FIGS. 3 and 4, the Gunn effect element of the present invention has excellent band characteristics, and its frequency characteristics extend toward higher frequencies.

For example, focusing on curves 7 and 7', the bandwidth of 3 dB reduction in oscillation output when only the short length is changed is approximately 6 GHz in the oscillator of the comparative example, whereas it is approximately 6 GHz when using the Gunn effect element of the present invention. With the previous oscillator, the frequency reached 14 GHz, demonstrating a significant improvement in band characteristics.

FIG. 5 shows the frequency characteristics obtained by changing the oscillation frequency by changing the short length and adjusting the admittance of the oscillation circuit to an optimum value.

In FIG. 5, a curve 10 shows the frequency characteristics of the oscillator using the Gunn effect element according to the example of the present invention, and a curve 11 shows the frequency characteristics of the oscillator of the comparative example.

As is clear from Figure 5. The output of the oscillator in the comparative example decreased rapidly as the frequency increased, and the output was 63 G.
On the other hand, the oscillator using the Gunn effect element according to the present invention has an oscillation frequency of 70 GHz or above.
It shows excellent frequency characteristics over z.

Furthermore, as is clear from FIGS. 3 to 5, the oscillation output of the oscillator using the Gunn effect element according to the present invention is not significantly lower than that of the oscillator of the comparative example.

The reason why the following effects of the present invention can be obtained is that the Gunn effect element according to the present invention has a large absolute value of negative resistance, so it is easy to construct an oscillation circuit with broadband characteristics, and This is thought to be because the change in resistance value is small, the impedance matching with the oscillation circuit is good, and the oscillation output decreases gradually with respect to frequency changes.

For example, the negative resistance value of the Gunn effect element of the above comparative example during high output operation is less than 15 Ω, and the negative resistance value changes by ±34% with respect to a frequency change of ±20%. The negative resistance value of Gunn effect element during high output operation is -11,20
Therefore, the change in negative resistance with respect to a frequency change of ±20% is only ±18%.

As a result of examining the electron concentration transition width by changing it, we found that the above-mentioned broadbanding effect was obtained when the electron concentration transition width was 40% of the operating crystal layer thickness.
% or more, it was found to be significant.

Figure 6 is a diagram showing the relationship between the diode area, oscillation output, and oscillation efficiency when the electron concentration transition width occupies 60% of the operating crystal layer thickness and the frequency is 65 GHz.
indicates the oscillation output, and the broken line η indicates the oscillation efficiency.

As is clear from the figure, the diode area is approximately 5.5X
The oscillation output and oscillation efficiency rapidly decrease as the diode area increases beyond the point of oscillation output P' and oscillation efficiency η' at 10''ffl.

At this time, the negative resistance at Niboshi 9 and η' is about -5
Since it is 0, it is determined that when the negative resistance becomes smaller than -50, the band characteristics deteriorate rapidly.

Figure 7 shows that the electron concentration transition width is 20% of the operating crystal layer thickness, 4
Negative conductance at 0% and 60% (-G
) and susceptance (B), where line X shows the case of 20%, line Y shows the case of 40%, and line Z shows the case of 60%.

Note that the negative resistance (6) is calculated from equation (1) using conductance (G) and susceptance (B).

R=(-G')/(G2+B2) ・・・・・・・・・
・ (1) From this, the negative resistance R becomes approximately -50 at the point Y' when the electron concentration transition width is 40% (g), and as the electron concentration transition width becomes larger than 40%, the negative resistance increases. is derived to be greater than 15Ω.

Therefore, when the electron concentration transition width becomes smaller than 40% of the operating crystal layer thickness, the absolute value of the negative resistance becomes small, and the change in the negative resistance value with respect to frequency changes becomes large, and due to their correlation, the band characteristics change. Deteriorates rapidly.

On the contrary, the entire active layer is an electron concentration transition region,
Gunn effect elements, which have a distribution in which the electron concentration gradually increases toward the substrate, have only a slight decrease in oscillation output;
It was found that it has extremely good band characteristics and enables oscillation at higher frequencies.

As described above, according to the present invention, it is possible to significantly improve the band characteristics and frequency characteristics of a solid-state oscillator without substantially reducing the oscillation output.

Although the above-mentioned effects of the present invention are remarkable when applied to millimeter-wave band Gunn effect elements, the present invention also has the following effects for other frequency bands:
It goes without saying that the band widening effect of the present invention can be obtained, and that the present invention can also be applied to Gunn effect elements using compound semiconductors other than GaAs crystals that can cause the Gunn effect.

[Brief explanation of drawings]

Figure 1 is a diagram showing the electron concentration distribution of a conventional Gunn effect element.
FIG. 2 is a diagram showing the electron concentration distribution of the Gunn effect element of the example of the present invention, FIG. 3 is a diagram showing the frequency characteristics of the oscillator of the example of the present invention, and FIG. 4 is a diagram showing the frequency characteristics of the oscillator of the comparative example. Figure 5 shows the frequency characteristics of the oscillators of the examples of the present invention and comparative examples, and Figure 6 shows the diode area, oscillation output, and FIG. 7 shows the relationship between negative conductance and susceptance when the electron concentration transition width occupies 20%, 40%, and 60% of the operating crystal thickness. 1 is a substrate, 2 is an active layer, 3 is an electrode layer, and 5 is an electron concentration transition region. 4 is a region where the electron concentration in the active layer is almost flat.

Claims (1)

[Claims] 1 In the active crystal layer, the electron concentration transition width on the side in contact with the high electron concentration substrate is 40% to 1% of the thickness of the active crystal layer.
A gun effect element characterized in that it occupies 00%.