Si-doping of MOVPE grown InP and GaAs by using the liquid Si source ditertiarybutyl silane

doi:10.1016/S0022-0248(98)00592-2

Journal of Crystal Growth

Volume 195, Issues 1–4, 15 December 1998, Pages 91-97

https://doi.org/10.1016/S0022-0248(98)00592-2 Get rights and content

Abstract

The liquid Si-compound ditertiarybutyl silane (DTBSi) has been investigated as a doping source for the metal organic vapour-phase epitaxy (MOVPE) of InP and GaAs using TBP or DTBP and TBAs as less hazardous group-V-sources. For both material systems the measured carrier concentration is directly proportional to the DTBSi/group-III-partial pressure ratio with a slope of unity. Uncompensated n-type InP as well as GaAs layers are achieved up to the 10¹⁸ cm⁻³ doping range. Additional calibrated SIMS-studies of InP layers show a coincidence of the Si-concentration in the InP layers with the measured net n-type carrier concentration within the experimental errors. With a reduction of the growth temperature from 610°C to 570°C a significant reduction of the Si-doping efficiency is observed. However, for temperature in excess of 610°C up to 700°C an almost constant doping efficiency for GaAs is obtained. For GaAs a slight reduction in Si-incorporation efficiency with increasing V/III-ratio is detected. The successful doping characteristics for GaAs have been applied to realize n-GaAs : Si Hall sensor device structures. The lateral homogeneity of the sheet resistance is evaluated as a function of the V/III-ratio and the substrate material. Under optimum conditions the normalized variance of the sheet resistance can be as low as 1%.

Introduction

The major n-type doping source for III/V-semiconductors is silicon (Si). For metalorganic vapour-phase epitaxy (MOVPE) up to now primarily hazardous, gaseous Si-sources like silane SiH₄ [1]and disilane Si₂H₆ [2]have been used. In recent years, the less hazardous, liquid P- and As-compound tertiarybutyl phosphine (TBP) and tertiarybutyl arsine (TBAs) are becoming more and more interesting as substitutes for the highly toxic, hydride gases PH₃ and AsH₃ for MOVPE. In order to establish an all liquid source MOVPE growth process, which would particularly simplify the MOVPE equipment, liquid Si-compounds like hexamethyl disilane ((CH₃)₆Si₂, HMDSi) [3], tetraethyl silane ((C₂H₅)₄Si, TeESi) [4]or tertiarybutyl silane (t-(C₄H₉)SiH₃, TBSi) [5]have been studied as possible doping sources. While HMDSi also leads to a significant incorporation of C, the two other sources show a significant temperature dependence in particular in the temperature range below 600°C.

Following the detailed investigations of the Si-incorporation in the SiH₄/TBAs material combination and the corresponding doping study using TBSi [5], the present investigations concentrate on the novel Si-doping source ditertiarybutyl silane (t-(C₄H₉)₂SiH₂, DTBSi). This compound has a lower vapour pressure as compared to TBSi and, thus, can be used in a more controlled way as doping source. The reaction chemistry in combination with TBAs is expected to be simplified as compared to the TeESi/TBAs material combination. In addition, there is a possibility that the decomposition of the DTBSi does not directly lead to the formation of SiH₄, as in the case of TBSi [5], thus possibly leading to a less temperature-sensitive incorporation behaviour. Therefore, we have studied the Si-doping incorporation using DTBSi for the MOVPE growth of InP in combination with TBP and ditertiarybutyl phosphine (DTBP) 6, 7and of GaAs in combination with TBAs. The doping incorporation as a function of the growth conditions is investigated by Hall as well as by secondary-ion mass spectrometry (SIMS) studies. The obtained results are applied to the realization of GaAs Hall sensor structures. The variation of the sheet resistance across the full 2″ wafer is presented and discussed.

Section snippets

Experimental procedure

The MOVPE growth experiments have been performed in a horizontal, IR-heated reactor system with sample rotation using the gas foil rotation principle (Aix 200, Aixtron Corp.). A reactor pressure of 100 mbar and a total flow of 6.800 sccm H₂ carrier gas have been applied. The trimethyl group-III compounds TMIn and TMGa have been used. The growth temperature has been chosen in the range of 550–610°C for InP using TBP or DTBP as P-compounds. The substrate temperature is calibrated with the

Results and discussion

The results of the Si-doping experiments for InP using DTBSi are presented in the first part of this main section. In the second part, the results of the Si-incorporation in GaAs during MOVPE growth using TBAs are described. The third part describes the doping incorporation efficiency as a function of growth temperature. Based on these findings GaAs : Si Hall sensor device layers are deposited on full 2″ wafers and their characteristic is evaluated and discussed.

Conclusions

With the aim of an all liquid source MOVPE process, the liquid Si-compound ditertiarybutyl silane (DTBSi) has been investigated as a doping source for InP and GaAs using TBP or DTBP and TBAs as less hazardous group-V-sources. Because of the common alkyl group of the Si- and the group-V-compounds a simplified reaction chemistry is expected. For both material systems the measured carrier concentration is directly proportional to the DTBSi/group-III-partial pressure ratio with a slope of unity.

Acknowledgements

The authors are indebted to Dr. M. Müller (Dept. of Chemistry, Philipps-University Marburg) for transfilling and for chemical analysis of the liquid Si-source ditertiarybutyl silane (DTBSi).The expert technical support of T. Ochs during the MOVPE investigations is gratefully acknowledged. Part of this work has been supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF).

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A wide range of n- and p-type doping levels in GaAs layers grown by chemical beam epitaxy is achieved by using H₂-diluted DTBSi and CBr₄ as gas precursors for Si and C, respectively. We show that the doping level can be varied by modifying either the concentration or the flux of the diluted precursor. Specifically, we demonstrate carrier concentrations of $7.8 \times 10^{17}$ – $1.4 \times 10^{19}$ cm⁻³ for Si, and $1 \times 10^{17}$ – $3.8 \times 10^{20}$ cm⁻³ for C, as determined by Hall effect measurements. The dependence of Si incorporation on the diluted-precursor flux is found to be linear. In contrast, we observe a superlinear behavior for C doping. The dependence of the electron and hole mobility values on the carrier concentration as well as the analysis of the layers by low-temperature (12 K) photoluminescence spectroscopy indicate that the use of H₂ for diluting DTBSi or CBr₄ has no effect on the electrical and optical properties of GaAs.
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Liquid Si ditertiarybutyl silane (DTBSi) metal-organic source was used as the Si dopant source for the growth of n-type GaN by metal-organic chemical vapor deposition (MOCVD) for the first time to replace the conventional gaseous Si sources like silane SiH₄ [K. Pakula, R. Bozek, J.M. Baranowski, J. Jasinski, Z. Liliental-Weber, J. Crystal Growth 267 (2004) 1] and disilane Si₂H₆ [L.B. Rowland, K. Doverspike, D.K. Gaskill, Appl. Phys. Lett. 66 (1995) 1495]. Electrical, structural, optical, and surface properties of the samples doped by DTBSi as well as an undoped control sample are determined by Hall, high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and atomic force microscopy (AFM) measurements respectively. A constant doping efficiency for GaN is obtained with carrier concentration up to 10¹⁸ cm⁻³. The typical HRXRD full-width at half-maximum values of symmetric (0 0 2) and asymmetric (1 0 2) planes are 284 and 482 arcsec, respectively. The near band edge PL intensity is found to be increased proportional to the doping concentration. Dark spot density is also determined from AFM measurement.
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¹: Present address: Aixtron GmbH, D-52053 Aachen, Germany.

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Si-doping of MOVPE grown InP and GaAs by using the liquid Si source ditertiarybutyl silane

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgements

J. Crystal Growth

J. Crystal Growth

J. Crystal Growth

J. Crystal Growth

J. Electrochem. Soc.

J. Appl. Phys.