JP2009016597A - Transistor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transistor element of high current gain. <P>SOLUTION: In the transistor device 1 in which a heterobipolar transistor 3 is formed on a substrate 2 and a high electron mobility transistor 4 is formed on the heterobipolar transistor 3, the layer thickness of the base layer 8 of the heterobipolar transistor 3 is 120 nm or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transistor element having a high current gain.

  The operation of the hetero bipolar transistor (HBT) is basically the same as that of a normal bipolar transistor (BJT). In the npn-type BJT, the amount of electrons flowing from the emitter to the collector is controlled by a base current (hole current), thereby operating as a transistor. That is, the collector current increases by increasing the Hall current. However, if the hole current is further increased, holes leak from the base toward the emitter, and the current amplification factor of the transistor decreases. However, in an npn type HBT using a semiconductor material having a large band gap for the emitter, a barrier is formed at the base-emitter interface, and leakage of holes to the emitter can be suppressed. Therefore, in the HBT, the collector current can be increased without reducing the current amplification factor.

As shown in FIG. 3, a conventional HBT element 301 has a semi-insulating GaAs substrate 302 with an n-type GaAs layer serving as a subcollector layer 303 having a thickness of 500 nm and an n-type GaAs layer serving as a collector layer 304 having a thickness. 700 nm thick, p-type GaAs layer serving as the base layer 305 is 50 nm thick, n-type In _x Ga _1-x P layer (x = 0.48) serving as the emitter layer 306 is 40 nm, and n-type serving as the emitter contact layer 307 The GaAs layer is 100 nm, the n-type IN _x Ga _1-x As layer (x = 0 → 0.5) to be the graded non-alloy layer 308 is 50 nm, and the n-type In _x Ga _1-x As layer is the uniform composition non-alloy layer 309. (X = 0.5) are stacked in order of 50 nm.

  On the other hand, a high electron mobility transistor (HEMT) has an InGaAs layer as a channel layer and an electron supply layer on both sides or one side of the channel layer. The heterojunction HEMT not only enables high-speed operation by taking advantage of the high-speed movement of electrons, but also enables high-power and high-efficiency operation in an ultra-high frequency band such as a microwave band.

As shown in FIG. 4, a conventional HEMT device 401, on a semi-insulating GaAs substrate 402, an undoped GaAs buffer layer 403, n-type _Al x _{Ga 1-x} As electron supply layer 404, an undoped _Al x _{Ga 1- x} As spacer layer 405, undoped In _x Ga _1-x As channel layer 406, undoped Al _x Ga _1-x As spacer layer 407, n-type Al _x Ga _1-x As electron supply layer 408, n-type GaAs cap layer 409 Are sequentially laminated.

  These transistor elements have been mainly used in power amplifiers for transmitting and receiving mobile terminals, but in recent years, it has become necessary to transmit and receive a large amount of various information such as moving images at high speed using only voice and data. For this reason, transmission power amplifiers, which are the parts that consume the most power among portable terminals, are also required to have high performance, operate at a low voltage, and reduce power consumption. These can meet the demand by increasing the efficiency of the power amplifier, but generally there is a problem that distortion of the output signal becomes large when the amplifier is operated with high efficiency. When a radio wave leaks to an adjacent communication channel due to distortion, the signal of the channel and the signal of the adjacent communication channel interfere with each other, and the transmission data becomes a different value.

  Therefore, the HBT and the HEMT are not connected and used, but the wiring is reduced by integrating the HBT and the HEMT to suppress power consumption and distortion of the output signal.

  In the power amplifier module 501 shown in FIG. 5, the input signal is amplified by the driving HEMT 502, and the amplified signal is further amplified by the output HBT 503 at the subsequent stage to be an output signal.

  In the transistor element disclosed in Patent Document 1, an HBT is formed on a GaAs substrate, and a HEMT is formed on the HBT.

JP 2006-228784 A

  However, if the HEMT is grown on the HBT after the HBT is grown on the GaAs substrate, the crystal deteriorates due to the growth temperature (high temperature) at that time, and the current gain of the HBT is lowered. That is, in the case of growing only the HBT, it is possible to prevent the deterioration of the HBT due to the growth temperature by lowering the temperature immediately after the growth of the HBT. However, if the HEMT is grown after the growth of the HBT, the HBT grows longer. The current gain decreases due to the loss of As upon exposure to temperature.

  Therefore, there is a demand for a transistor element in which the current gain does not decrease even if the HEMT is grown on the HBT after the HBT is grown on the GaAs substrate.

  Accordingly, an object of the present invention is to solve the above problems and provide a transistor element having a high current gain.

  In order to achieve the above object, the present invention provides a transistor element in which a heterobipolar transistor is formed on a substrate, and a high electron mobility transistor is formed on the heterobipolar transistor. Is 120 nm or more.

  The substrate may be a semi-insulating compound substrate such as GaAs or InP.

  The substrate may be a silicon substrate.

  The present invention exhibits the following excellent effects.

  (1) Current gain is high.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a transistor element 1 according to the present invention is a transistor in which a heterobipolar transistor (HBT) 3 is formed on a substrate 2 and a high electron mobility transistor (HEMT) 4 is formed on the HBT 3. In the element 1, the layer thickness of the base layer 8 of the HBT 3 is 120 nm or more.

  A detailed structure of the transistor element of the present invention will be described together with a manufacturing method.

On the semi-insulating GaAs substrate 2, by epitaxial growth, the un-GaAs layer that becomes the buffer layer 5 has a thickness of 100 nm, the n-type GaAs layer that becomes the subcollector layer 6 has a thickness of 500 nm, and the n-type GaAs layer that becomes the collector layer 7 700 nm, the p-type GaAs layer serving as the base layer 8 is 120 nm thick, the n-type In _x Ga _1-x P layer (x = 0.48) serving as the emitter layer 9 is 40 nm thick, and the n-type serving as the ballast layer 10 The type GaAs layer is 100 nm thick, the un-Al _x Ga _1-x As layer (x = 0.28) serving as the buffer layer 11 is 500 nm thick, and the n-type Al _x Ga _1-x As serving as the electron supply layer 12. The layer (x = 0.3) has a thickness of 30 nm, the un-Al _x Ga _1-x As layer (x = 0.3) serving as the spacer layer 13 has a thickness of 10 nm, and the channel layer 14 In _x Ga _{1− x} s layer (x = 0.18) with a thickness of 15 nm, a spacer layer _{15 un-Al x Ga 1-} x As layer (x = 0.3) thickness 10 nm, the electron supply layer 16 n-type In _{The x} Ga _1-x P layer (x = 0.48) is 30 nm thick, the un-GaAs layer that is the Schottky layer 17 is 30 nm thick, and the n-type In _x Ga _1-x P layer that is the stopper layer 18 ( x = 0.48) are stacked in a thickness of 10 nm and n-type In _x Ga _1-x As layers (x = 0.5) to be non-alloy layers 19 and 20 are stacked in order of 50 nm in thickness, respectively. The transistor element 1 is manufactured.

When this transistor element 1 was subjected to an operation test, the base resistance of the HBT 3 was 220 Ω / sq. An amplification effect with a current gain of 120 (current density 1 kA / cm ² ) was obtained. The mobility of HEMT4 was 4000 cm ² / V · s, the sheet carrier concentration was 2.1 × 10 ¹² cm ⁻² , and the pinch-off voltage was −0.5 V.

  Next, the thickness of the base layer was changed from less than 120 nm in the prior art to 120 nm or more according to the present invention, and other transistor conditions were manufactured under the same conditions. The current gain (current amplification factor) was examined by an operation test. The result is shown in FIG.

  As shown in FIG. 2, there is a relationship between the thickness of the base layer and the current gain (current amplification factor). By increasing the thickness of the base layer, the current gain increases with the same base resistance. When the layer thickness is 120 nm or more, the current gain hardly changes. From this, it can be concluded that a sufficiently high current gain can be obtained if the thickness of the base layer is 120 nm or more. The base resistance is determined by the product of the base layer thickness and the sheet carrier concentration. For example, when the layer thickness is increased from 100 nm to 120 nm, the base resistance is kept the same by reducing the sheet carrier concentration by 20% accordingly.

  According to the present invention, in the transistor element 1 in which the HBT 3 is formed on the substrate 2 and the HEMT 4 is formed on the HBT 3, the thickness of the base layer 8 of the HBT 3 is 120 nm or more. The current gain can be increased as compared with the conventional transistor element that is less than 120 nm.

  In the above embodiment, a semi-insulating GaAs substrate is used as the substrate, but the present invention can also be applied to Si substrates and InP substrates.

  According to the present invention, when used in a transmission power amplifier, a transistor element that operates at a low voltage, suppresses distortion of an output signal, can reduce power consumption, and does not reduce current gain is provided. Can do. This is because the HBT 3 and the HEMT 4 are formed on the same substrate 2 and the wiring connecting the HBT 3 and the HEMT 4 can be omitted, so that power consumption is reduced and distortion of the output signal is suppressed.

It is a laminated structure figure of the transistor element which shows one Embodiment of this invention. It is a graph which shows the relationship between the layer thickness of a base layer, and a current gain. It is a laminated structure figure of an HBT element. It is a laminated structure figure of a HEMT element. It is a circuit diagram of the conventional power amplifier module.

Explanation of symbols

1 Transistor element 2 Semi-insulating GaAs substrate 3 HBT
4 HEMT
5 buffer layer 6 subcollector layer 7 collector layer 8 base layer 9 emitter layer 10 ballast layer 11 buffer layer 12 electron supply layer 13 spacer layer 14 channel layer 15 spacer layer 16 electron supply layer 17 Schottky layer 18 stopper layer 19 non-alloy layer 20 Non-alloy layer

Claims (3)

  A transistor element in which a heterobipolar transistor is formed on a substrate, and a high electron mobility transistor is formed on the heterobipolar transistor, wherein the layer thickness of the base layer of the heterobipolar transistor is 120 nm or more element.   2. The transistor element according to claim 1, wherein the substrate is a semi-insulating compound substrate such as GaAs or InP.   2. The transistor element according to claim 1, wherein the substrate is a silicon substrate.

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