JP4901110B2 - Compound semiconductor epitaxial crystal and growth method thereof - Google Patents

Description

  The present invention uses a chemical vapor deposition apparatus for vapor-depositing a thin film, and in particular, metalorganic vapor phase growth for growing a plurality of compound semiconductor epitaxial films such as indium phosphide (InP) and indium gallium arsenide (InGaAs). The present invention relates to a technique applied to the method (MOCVD).

  Conventionally, an epitaxial crystal substrate used for an electronic device such as HBT (heterojunction bipolar transistor) or HFET (heterojunction field effect transistor) has an epitaxial layer grown on a compound semiconductor substrate such as InP by MOCVD or MBE. It is common to be manufactured. For example, an epitaxial crystal substrate for HBT is manufactured by sequentially growing an n-type collector layer, a p-type base layer, an n-type emitter layer, and an n-type contact layer on an InP substrate. Among these, the crystallinity of the p-type base layer and the steepness of the pn junction interface are the keys to improving the HBT characteristics.

As an example, the p-type base layer can be made of InGaAs, and a technique of adding C using CBr ₄ or CCl ₄ as a dopant at this time is often used. However, it is difficult for InGaAs to add C compared to GaAs. That is, since the bond energy between In and C is smaller than the bond energy between Ga and C, it is estimated that InGaAs is less likely to incorporate C into the crystal than GaAs (Non-patent Document 1).

On the other hand, when adding C to InGaAs, it is known that the addition efficiency increases as the growth temperature decreases. For example, in Patent Document 1, when C-doped InGaAs is grown epitaxially, the substrate temperature is grown by 50 to 100 ° C. lower than the substrate temperature (500 ° C.) when C-doped GaAs is grown. Yes. Specifically, on an InP substrate, after growing the collector layer and the substrate temperature above 550 ° C., it is grown InGaAs layer of C added while the substrate temperature is lowered T _B to four hundred twenty to four hundred fifty ° C. or less, Thereafter, a technique for manufacturing an HBT having a C-doped InGaAs layer as a p-type base layer by growing an emitter layer in a state where the substrate temperature is raised to T _B + 60 ° C. or less is disclosed.

In addition, since the efficiency of adding C to InGaAs is extremely low, it is necessary to increase the flow rate of the dopant (for example, CBr ₄ ) to the same flow rate as that of the group III source gas (TMGa or TMIn). Since CBr ₄ and In react with each other to reduce the In ratio in the crystal, further adjustment of the flow rate of TMIn is necessary to adjust it (Non-patent Document 2).
Japanese Patent No. 3502267 Journal of Growth, 200 (1999), pp599-602 2003IPRM, pp418-421

By the way, even if the InGaAs layer is grown and C is taken into the crystal, it is not electrically activated due to the hydrogen passivation of the acceptor level or the absence of the C atom in the group III site. Even when × 10 ¹⁹ cm ^{−3 is} added, the carrier concentration immediately after the growth is only about 2 × 10 ¹⁸ cm ⁻³ . In this case, a high-concentration p-type conductive layer can be obtained only by activating C as an acceptor by heat treatment or the like.

  However, since the C-doped InGaAs base layer grown at a low temperature has a relatively low resistance to heat treatment at higher temperatures, the crystallinity of the base layer and the steepness of the pn junction may be impaired during this heat treatment. . In the technique disclosed in Patent Document 1, the substrate temperature when the emitter layer is grown on the InGaAs base layer is higher than the substrate temperature when the base layer is grown. There is also a possibility that the steepness of the bonding is impaired.

  Further, the technique of Non-Patent Document 2 has a problem that it is difficult to narrow down the growth conditions because the addition of C to InGaAs requires an adjustment that does not need to be taken into consideration in the ordinary MOCVD method.

  The present invention is an epitaxial crystal in which a p-type conductive layer is composed of a compound semiconductor layer containing C-doped InGaAs as a main component, and is excellent in the crystallinity of the p-type conductive layer and the steepness of the pn junction, and is an electron such as HBT. An object is to provide an epitaxial crystal useful as a substrate for a device.

The present invention has been made to solve the above problems, and a p-type conductive layer mainly composed of InGaAs in which carbon is added as a p-type impurity by supplying a halogenated carbon gas onto a compound semiconductor substrate. And a p-type conductive layer containing 0.5 to 10 mol% of antimony and a carbon addition rate of 0.04 to 0.06%. , wherein the activation ratio of carbon 20 to 50%, the carrier concentration of carbon is ^{1 × 10 19 ~4 × 10 19} cm -3.

  For example, the p-type conductive layer is used as a base layer of a heterojunction bipolar transistor. The p-type conductive layer is used as a contact layer with a metal film that becomes an electrode of the p-type conductive portion of the electronic device.

  In a method for growing a compound semiconductor epitaxial crystal in which a device structure including a p-type conductive layer mainly composed of InGaAs doped with carbon as a p-type impurity is formed on a compound semiconductor substrate, a chemical vapor deposition method is used. When the p-type conductive layer is grown by supplying a Group 15 (5B) source material containing arsenic and antimony and a Group 13 (3B) source material containing indium and gallium, the 15th (5B) The ratio of the gas flow rate of the Group raw material to the gas flow rate of the Group 13 (3B) raw material (Group V gas flow rate / Group III gas flow rate ratio) was set to be 1 or more and 20 or less. Furthermore, the substrate temperature during the growth of the p-type conductive layer was set to 450 ° C. or more and 500 ° C. or less.

  That is, in growing the p-type conductive layer, the growth conditions for growing InGaAs, which has been conventionally used as the p-type conductive layer, can be applied. Even if the substrate temperature during growth is as described above, the carbon addition efficiency to InGaAsSb as the p-type conductive layer is high, and the activation rate of the added carbon is also high.

Below, the background that led to the completion of the present invention will be described.
The inventors of the present invention have found that GaAsSb is lattice-matched with the InP substrate at a molar fraction of Sb of about 0.5, and that the addition efficiency and activation rate of C are relatively high. Attention has been focused on GaAsSb-based compound semiconductors in place of conventionally used InGaAs.

However, it is known that the epitaxial growth of GaAsSb requires that the V group gas flow rate / Group III gas flow rate ratio be close to 1 by including Sb, unlike that of GaAs. However, as a source gas for the group V component Sb and As, usually, an organic metal such as TMSb is used for Sb and a hydride such as AsH ₃ is used for As, and the respective decomposition reactions do not proceed uniformly in the reaction chamber. Therefore, the Sb / As ratio tends to vary within the substrate of the obtained GaAsSb epitaxial layer. Therefore, there is a problem that it is difficult to control composition uniformity and the like.

In addition, the relationship (distribution coefficient) between the gas composition ratio and the solid phase composition ratio is not linear in the incorporation into the epitaxial layer. As a result of the experiment, it was found that the solid phase composition changed greatly depending on the AsH ₃ gas flow rate, and the contribution of the TMSb gas flow rate was small. This behavior further makes it difficult to control the composition uniformly.

  On the other hand, when manufacturing a device such as HBT using GaAsSb as a material, an etchant suitable for an existing material (such as InP or InGaAs) cannot be etched cleanly as an etchant (etching solution) for performing mesa etching in the manufacturing process. Therefore, there is a problem that it is necessary to develop a new etching solution that is completely different from the conventional one.

  Therefore, by applying InGaAsSb obtained by adding Sb to InGaAs, it is not possible to form a p-type conductive layer (such as a base layer) that can increase the C addition efficiency and can be etched in a later process by a method similar to the conventional method. The following experiment was conducted.

First, an InP layer serving as a buffer layer was grown at a substrate temperature of 600 ° C. on a semi-insulating InP substrate by MOCVD. Next, the substrate temperature was lowered to 450 to 500 ° C., and a C-doped InGaAsSb layer was grown. The substrate temperature at this time is approximately ˜30 ° C. higher than the substrate temperature (450 ° C. or less) when the conventional InGaAs layer is grown. Thereafter, the substrate temperature was raised to 550 ° C. while flowing AsH ₃ / H ₂ so that As was not decomposed and desorbed from the surface of the epitaxial film, and an InP cap layer was grown.

In the epitaxial growth, TMIn and TMGa were used as Group III materials, PH ₃ , AsH ₃ and TMSb were used as Group V materials, and CBr ₄ was used as a dopant gas. In addition, the composition of InGaAsSb could be precisely controlled by accurately measuring the amount of raw material supplied. The pressure in the growth vessel was 60 Torr, and the flow of the reaction chamber was made uniform by flowing 30 slm using hydrogen purified by the Pb film as a carrier gas. For CBr ₄ , the supply amount was controlled by bubbling hydrogen gas as a carrier gas after immersing a raw material bottle in a thermostatic bath at a temperature of 30 ° C. and controlling the vapor pressure.

  An epitaxial crystal having a p-type conductive layer made of InGaAsSb was produced by the growth method described above, and the film thickness, electrical characteristics (Hall effect, etc.), lattice mismatch (X-ray rocking curve), etc. were measured. ,evaluated. As a result, when the p-type conductive layer is composed of InGaAsSb obtained by adding a small amount (for example, 10 mol%) of Sb to InGaAs, unlike the growth conditions for growing GaAsSb, the growth conditions for growing InGaAs are extended. It was found that the growth conditions can be set near the line. Specifically, in the case of GaAsSb, the V group gas flow rate / Group III gas flow rate ratio needs to be approximately 1, whereas in the case of InGaAsSb, the growth conditions of InGaAs are almost the same. A good epitaxial crystal could be grown by setting the group III gas flow ratio in the range of 1 or more and 20 or less.

  Further, epitaxial crystals were produced by changing the Sb content in InGaAsSb, and the C addition rate, carrier concentration, activation rate, and etching residue were measured and evaluated for this crystal. As a result, it was found that when the Sb content (mol%) in InGaAsSb is increased, the C addition efficiency and the activation rate are increased.

Specifically, when the Sb content of InGaAsSb was 0 mol%, the activation rate was almost 0, whereas at 0.1 mol%, it was 10%, and at 0.5 mol%, it was 20%. Further, when the Sb content was 0.5 mol%, the carrier concentration was 4 × 10 ¹⁹ cm ⁻³ , and a carrier concentration of 2 × 10 ¹⁹ cm ⁻³ or more required for the p-type conductive layer could be achieved. Furthermore, when the Sb content was 10 mol%, the activation rate of C was 50%, 30 mol% was 90%, and 50 mol% was 100%.

  Moreover, the addition efficiency was 1 to 3 times that in the case where Sb was not included, and it was not observed that the addition efficiency decreased due to the effect of Sb.

  On the other hand, in the range where the Sb content is relatively low (10% or less), it is possible to perform relatively fine mesa etching using an etchant (phosphoric acid type, citric acid type, ammonia type) for mesa etching of InGaAs. The width was at a level with no problem. On the other hand, when the Sb content is 30% or more, Sb is mixed without being dissolved in the etchant, which causes pattern foreign matters in the device manufacturing process, and it has been found that the conventional etchant cannot be used.

  Further, it was found that the uniformity of the composition and doping amount deteriorates in the range where the Sb content is relatively high (30% or more).

Table 1 shows the characteristics of InGaAsSb with respect to the Sb content. As shown in Table 1, when the Sb content is 0.5 mol% or more, the activation rate of C becomes 20% and the target carrier concentration (2 × 10 ¹⁹ cm ⁻³ ) can be achieved. In addition, it was found that a p-type conductive layer (base layer or contact layer) that can be mesa-etched with an etchant that has been conventionally used can be produced by setting the content to 10 mol% or less.

According to the present invention, in a compound semiconductor epitaxial crystal in which a device structure including a p-type conductive layer mainly composed of InGaAs doped with carbon as a p-type impurity is formed on a compound semiconductor substrate, the p-type conductive layer is formed. Has an antimony content of 0.5 to 10 mol%, so that the activation rate of C is increased, and the target carrier concentration (2 × 10 ¹⁹ cm ⁻³ ) can be easily achieved. Mesa etching with the etchant used in the above is possible.

  Furthermore, by applying InGaAsSb as the p-type conductive layer, the growth temperature can be increased by about 50 ° C. compared to the growth temperature of InGaAs. Even when the emitter layer is grown after the growth of the p-type conductive layer (base layer), the growth temperature is increased. Therefore, the thermal deterioration is reduced as compared with the case where the emitter layer is grown after the growth of InGaAs. In addition, since C-doped InGaAsSb has a high C activation rate, it is not necessary to perform the heat treatment conventionally performed after the growth of the p-type conductive layer in order to activate C. Therefore, the crystallinity of the p-type conductive layer and the steepness of the pn junction can be avoided, so that an epitaxial crystal suitable for use in an electronic device such as an HBT is obtained.

  In addition, since the growth time can be shortened by reducing the adjustment range of the growth temperature, and the heat treatment step for increasing the C activation rate can be omitted, the production efficiency is greatly improved.

Hereinafter, as a preferred embodiment of the present invention, a method for manufacturing an InP / InGaAsSb-based HBT will be specifically described with reference to the drawings.
First, the substrate temperature of the semi-insulating InP substrate 1 was raised to 550 ° C., and a silicon-added n-type InGaAs layer 2 serving as a contact layer with the collector electrode was grown on the substrate by MOCVD. Next, an undoped InGaAs layer 3 was formed as a collector layer.

Next, the supply of TMGa and TMIn is stopped, the growth of the collector layer 3 is interrupted, the substrate temperature is lowered to 450 to 500 ° C. while AsH ₃ is supplied, and then the supply of the source gas is resumed to form the base layer A C-doped p-type InGaAsSb layer 4 (p-type conductive layer) was grown. The growth temperature at this time is about ˜50 ° C. higher than the growth temperature (450 ° C. or lower) when a C-doped p-type InGaAs layer is grown as a conventional base layer. Also, CBr ₄ is used as a dopant for the p-type impurity, and the supply amount of CBr ₄ is controlled by bubbling hydrogen gas as a carrier gas after immersing the raw material bottle in a thermostatic bath at a temperature of 30 ° C. and controlling the vapor pressure. did.

Next, after the growth of the base layer 4 was completed, the supply of TMGa, TMIn, and CBr ₄ was stopped, the growth of the base layer 4 was interrupted, and the substrate temperature was raised to 550 ° C. while AsH ₃ was supplied. Then, after the substrate temperature was set to 550 ° C., a source gas was supplied to sequentially grow a silicon-added n-type InP layer 5 as an emitter layer and a silicon-added n-type InGaAs layer 6 as a contact layer with the emitter electrode. Through these growth steps, an epitaxial crystal that can use the compound semiconductor layer 4 mainly composed of C-doped InGaAs as shown in FIG. 1 as the base layer of the HBT is produced.

In the above epitaxial growth, TMIn and TMGa are used as Group III materials, PH ₃ , AsH ₃ and TMSb are used as Group V materials, CBr ₄ is used as an n-type dopant gas, and disilane (Si ₂ H is used as an n-type dopant gas. ₆ ) was used. The pressure in the growth vessel was 60 Torr, and the flow of the reaction chamber was made uniform by flowing 30 slm using hydrogen purified by the Pb film as a carrier gas.

  In the growth method described above, the composition of InGaAsSb can be precisely controlled by accurately measuring the supply amount of the organometallic raw material. Specifically, in this embodiment, the Sb content of the p-type base layer was set to 10 mol% by setting the group V gas flow rate / group III gas flow rate ratio to 3.

Moreover, in the obtained epitaxial crystal, the C carrier concentration of the base layer 4 made of InGaAsSb was 1 × 10 ¹⁹ cm ⁻³ and the C activation rate was 50%. Further, etching can be performed without any problem by using an etchant (phosphoric acid-based, citric acid-based, ammonia-based) conventionally used for etching InGaAs. Moreover, it became possible to obtain an activation rate of almost 100% by post-annealing shorter than before.

  Furthermore, when an electrode was provided to produce an HBT and its characteristics (for example, current amplification factor) were evaluated, it was confirmed that high device characteristics could be obtained. That is, it can be said that the epitaxial crystal obtained by the growth method described above is excellent in crystallinity of the base layer and steepness of the pn junction, and has been confirmed to be suitable as a substrate for an electronic device such as HBT.

As mentioned above, although the invention made by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.
For example, in the above embodiment, the group V gas flow rate / group III gas flow rate ratio is 3, but the group V gas flow rate / group III gas flow rate ratio can be set in the range of 1-20. That is, the growth conditions can be made almost the same as the growth conditions of InGaAs conventionally used as the p-type conductive layer.

In addition, by setting the Sb content of the p-type base layer in the range of 0.5 to 10 mol%, the C activation rate is increased and the target carrier concentration (2 × 10 ¹⁹ cm ⁻³ ) can be easily obtained. This can be achieved, and mesa etching using an etchant conventionally used for etching InGaAs can be performed.

  In the above embodiment, the base layer (p-type conductive layer) is made of C-doped InGaAsSb. However, a contact layer with the base electrode may be further provided, and this layer may be made of InGaAsSb.

It is explanatory drawing which shows the laminated structure of the epitaxial crystal for HBT to which this invention is applied.

Explanation of symbols

1 Semi-insulating substrate 2 Contact layer with collector electrode 3 Collector layer 4 Base layer (C-doped p-type InGaAsSb)
5 Emitter layer 6 Contact layer with emitter electrode

Claims (5)

A compound semiconductor epitaxial crystal in which a plurality of epitaxial layers including a p-type conductive layer mainly composed of InGaAs doped with carbon as a p-type impurity by supplying a carbon halide gas on a compound semiconductor substrate are stacked. And
The p-type conductive layer contains 0.5 to 10 mol% of antimony, has a carbon addition rate of 0.04 to 0.06%, a carbon activation rate of 20 to 50%, and a carbon carrier concentration of 1. compound semiconductor epitaxial crystal, which is a ^{× 10 19 ~4 × 10 19 cm} -3.   The compound semiconductor epitaxial crystal according to claim 1, wherein the p-type conductive layer is a layer used as a base layer of a heterojunction bipolar transistor.   The compound semiconductor epitaxial crystal according to claim 1, wherein the p-type conductive layer is a layer used as a contact layer with a metal film serving as an electrode of a p-type conductive portion of an electronic device. In the growth method of the compound semiconductor epitaxial crystal in any one of Claim 1 to 3,
When the p-type conductive layer is grown by supplying a Group 15 (5B) source material containing arsenic and antimony and a Group 13 (3B) source material containing indium and gallium by chemical vapor deposition.
A method of growing a compound semiconductor epitaxial crystal, wherein a ratio of a gas flow rate of the Group 15 (5B) source material to a gas flow rate of the Group 13 (3B) source material is 1 or more and 20 or less.   The method for growing a compound semiconductor epitaxial crystal according to claim 4, wherein a substrate temperature during the growth of the p-type conductive layer is set to 450 ° C. or more and 500 ° C. or less.

Images