Growth of GaP Layers from Thin Aliquot Melts: Liquid Phase Epitaxy as a Commercial Process

Abstract

The highest electroluminescent device performance in most III-V semiconductor materials was obtained on thin layers grown by liquid phase epitaxy (LPE). LPE has not been developed, however, as a commercial process. From a comparison of the factors affecting layer quality and process economy, it is concluded that a commercial LPE process Iavors the use of thin melts (possibly discarded after deposition), should provide substrate protection prior to deposition, and should be able to terminate LPE growth. ,%. system has been designed in which a large volume of a saturated melt is sectioned into many small but equal thin melts (aliquot) for each substrate. The key to forming aliquots is wetting the substrate by the large volume of the melt in an apparatus constructed of nonwetted materials. The application of the above concepts to a multislice operation is described. Gallium phosphide LPE layers were grown in a single slice aliquot system from melts of 0.5-12 mm in thickness at cooling rates of 0.6~176Constitutional supercooling had no effect on the surface quality of the grown layers. The layers were degraded, however, if the substrates were thermally etched prior to deposition. High deposition efficiency and excellent thickness control were obtained for layers grown from thin melts. The deposition efficiency for layers grown from thick melts is limited by diffusion controlled mass transport in the melt. The diffusion coefficient of P in Ga has been evaluated at ~100O~ and no spontaneous nucleation was observed in melts supercooled by less than approximately 15~The first commercial application of liquid phase epitaxy (LPE) in the semiconductor industry was the manufacture of germanium alloy junction transistors (1). Since this process required the LPE growth on each individual device, it could not compete economically with gas phase epitaxy or diffusion used in batch processing over the entire semiconductor wafer. The interest in LPE was revived with the successful utilization of this process for III-V semiconductors. Some high performance devices could be achieved only through the application of this method. Two outstanding examples are GaP LED's (2, 3) and heterostructure GaAs, GaA1As lasers (4). Other device applications are discussed in a recent review article (5).The quest for improved device performance, increased yield, and the requirements for batch processing have placed increased demands on the LPE technology. Higher quality material is demanded at lower cost. The purpose of this paper is to show, using GaP LED material as an example, that both requirements can be met simultaneously.To produce p-n junctions in GaP with high electroluminescent efficiency, two consecutive LPE layers must be grown, each approximately 25# thick. Layer growth is accomplished by the depletion of a saturated Ga melt; the dopants are introduced into the melt prior to deposition.High-quality devices impose the following material requirements: (i) uniform distribution of dopants in the plane of the junction with only a limited varia...

Investigation of Melt Carry‐Over during Liquid Phase Epitaxy: I . Growth of Indium Phosphide

“…This effect, however, is overcome by pressure head effects for melt heights greater than -0.25 cm. It is important to point out that the dependence Of melt carry-over on melt height strongly suggests that confined melts (14) should significantly reduce melt carry-over, provided that a pressure head is not maintained on the confined melt by weights or other configurations such as a baffled solution holder. It is therefore desirable that boat configurations which minimize melt pressure head and, hence, carry-over be utilized in the LPE growth of InGaAsP.…”

“…[5]. It is important to point out that the dependence Of melt carry-over on melt height strongly suggests that confined melts (14) should significantly reduce melt carry-over, provided that a pressure head is not maintained on the confined melt by weights or other configurations such as a baffled solution holder. [10] of the theoretical model is applicable.…”

Toward Exotic Silicon Doping with a Low Thermal Budget and Flexible Profile Control by Liquid-Phase Epitaxy

“…GaAs grown by LPE resulted in a thickness variation of 5% over 80% of the area of a 1 cm 2 sample . Additionally, a thickness variation between 3 and 10% has been demonstrated in a doped LPE layer across a substrate of 2.5 cm diameter for melt thicknesses up to 1 mm …”

“…11 Additionally, a thickness variation between 3 and 10% has been demonstrated in a doped LPE layer across a substrate of 2.5 cm diameter for melt thicknesses up to 1 mm. 12 Liquid-phase epitaxy (LPE) has been demonstrated with a boron-metal paste on interdigitated back-contact solar cells with a remarkable spatial accuracy and with region dimensions down to 120 μm. 13 This suggests the feasibility of LPE doping (LPED) for selective emitter formation, which has become an important aspect in the development of modern solar cell technologies.…”