R. T. Lee

Band-gap control of GaInP using Sb as a surfactant

The use of surfactants to control specific aspects of the vapor-phase epitaxial growth process is beginning to be studied for both the elemental and III/V semiconductors. To date, most reported surfactant effects for semiconductors relate to the morphology of the growing films. However, semiconductor alloys with CuPt ordering exhibit much more dramatic effects. The change in the CuPt order parameter induced by the surfactant translates into a marked change in the band-gap energy. Previous work concentrated on the effects of the donor tellurium. Te is less than ideal as a surfactant, since the change in band-gap energy is coupled to a large change in the conductivity. This letter presents the results of a study of the effects of an isoelectronic surfactant on the ordering process in GaInP. Sb has been found to act as a surfactant during organometallic vapor-phase epitaxial growth. At an estimated Sb concentration in the solid of 1×10−4, order is eliminated, as indicated by the band-gap energy. Surface phot...

The use of a surfactant (Sb) to induce triple period ordering in GaInP

A surfactant is used to induce an ordered structure in an epitaxial layer. The addition of small amounts of triethylantimony during the organometallic vapor phase epitaxy growth of GaInP on (001) GaAs substrates is shown to remove CuPt ordering with a resultant increase in band gap energy. Increasing the concentration of Sb in the vapor beyond a critical Sb to P ratio [Sb/P(v)] of 4×10−4 gives a reversal of this behavior. The band gap energy is observed to decrease by 50 meV at a concentration of Sb/P(v)=1.6×10−3, coincident with the formation of an ordered phase with a period triple the normal lattice spacing along the [111] and [111] directions. The formation of this new ordered structure is believed to be related to high concentrations of Sb on the surface, which leads to a change in the surface reconstruction from (2×4)-like to (2×3)-like, as indicated by surface photoabsorption performed in situ.

Surfactant controlled growth of GaInP by organometallic vapor phase epitaxy

The effect of the surfactant Sb has been studied for GaInP semiconductor alloys grown by organometallic vapor phase epitaxy. Dramatic changes in the optical and electrical properties of GaInP with CuPt ordering have been observed. A small concentration of triethylantimony (TESb) in the vapor is found to cause Sb to accumulate at the surface. In situ surface photoabsorption analysis indicates that Sb changes the surface bonding by replacing the [110] P dimers that are responsible for the formation of the CuPt structure during growth with [110] Sb dimers. As a result, the degree of order for the GaInP layers is decreased, as shown by transmission electron diffraction studies. The 20 K photoluminescence spectra show a 131 meV peak energy increase for GaInP layers grown on vicinal substrates when a small amount of Sb [Sb/P(v)=4×10−4] is added to the system during growth. The use of surfactants to control specific properties of materials is expected to be a powerful tool for producing complex structures. In ...

Bi surfactant effects on ordering in GaInP grown by organometallic vapor-phase epitaxy

The effect of the isoelectronic surfactant Bi on surface structure and ordering has been studied for GaInP semiconductor alloys grown by organometallic vapor-phase epitaxy. A small amount of Bi (trimethylbismuth) added during growth is found to result in disordering for layers grown using conditions that would otherwise produce highly ordered materials. An order of magnitude increase in the step velocity was observed by atomic-force microscopy. Bi completely eliminates three-dimensional islands on the singular (001) surface.

Bi surfactant control of ordering and surface structure in GaInP grown by organometallic vapor phase epitaxy

The surfactant Bi has been added during organometallic vapor phase epitaxial growth (OMVPE) of GaInP using the precursor trimethylbismuth. The addition of a small amount of Bi during growth results in disordered material using conditions that would otherwise produce highly ordered GaInP. Significant changes in the surface structure are observed to accompany the disordering. Atomic force microscopy measurements show that Bi causes an order of magnitude increase in step velocity, leading to the complete elimination of three-dimensional islands for growth on singular (001) GaAs substrates, and a significant reduction in surface roughness. Surface photoabsorption measurements indicate that Bi reduces the number of [110] P dimers on the surface. Secondary ion mass spectroscopy measurements reveal that the Bi is rejected from the bulk, even though it changes the surface reconstruction. Clearly, Bi acts as a surfactant during OMVPE growth of GaInP. The difference in band gap energy caused by the reduction in or...

Sb enhancement of lateral superlattice formation in GaInP

Epitaxial layers of GaInP were grown by organometallic vapor phase epitaxy with small amounts of TESb added to control the surface bonding. Above a concentration of Sb/III(v)=0.016, 12 K photoluminescence measurements show that the band gap is reduced, as compared to completely disordered GaInP, by Sb addition and that polarization along the [110] direction is as much as 41 times larger than along [110]. Transmission electron microscopy results show a lamellar domain structure in the [110]-zone axis dark-field images with a period of 120 nm. Atomic force microscopy shows surface undulations with the same period along the [110] direction. The results demonstrate an increase in the magnitude of the presence of lateral composition modulation with increasing Sb concentration.

Effect of surfactant Sb on carrier lifetime in GaInP epilayers

Samples of Ga0.52In0.48P grown on (001) GaAs with small amounts of surfactant Sb were investigated using time-resolved photoluminescence. All samples show a luminescence that may be fit to a two-stage exponential decay with a fast and a slow lifetime. For growth without Sb (Sb/III(v)=0), the sample shows a strong CuPtB ordering and a fast component lifetime of 7 ns. As the Sb concentration is increased, the degree of order is reduced, with a consequent increase in band gap energy. In the highest band gap material, produced at Sb/III(v)=0.016, the fast lifetime is 2.9 ns, an order of magnitude larger than published values for GaInP disordered by misorienting the substrate. Increasing the Sb further causes the band gap energy to decrease due to the onset of composition modulation. At Sb/III(v)=0.064, the fast component lifetime decreases to 0.79 ns. Samples grown with Sb/III(v)>0.016 show a lifetime that depends on energy and is fit well by a model of localized excitons.

Pyrolysis of tertiarybutylamine alone and with trimethylgallium for GaN growth

Abstract New nitrogen precursors that pyrolyze at low temperatures are desired to replace NH 3 for the organometallic vapor phase epitaxial growth of GaN and, especially, GaInN. Tertiarybutylamine (TBAm) is a candidate having a high vapor pressure that is relatively safe compared with other potential N sources. In order to test the suitability of TBAm for the growth of GaN, the pyrolysis was studied in He and H 2 ambients. The results of co-pyrolysis studies of TBAm plus trimethylgallium are also reported. The pyrolysis reactions are relatively complex. In a hydrogen ambient, the pyrolysis of TBAm alone proceeds mainly via production of t-butyl and NH 2 radicals. Co-pyrolysis studies show that an adduct is formed at low temperatures, with elimination of CH 4 . At higher temperatures, the adduct dissociates and co-pyrolysis proceeds mainly as for the individual precursors. TMGa pyrolysis results in the formation of Ga droplets.

Time dependent surfactant effects on growth of GaInP heterostructures by organometallic vapor phase epitaxy

It has been shown that adding the surfactant Sb during growth eliminates ordering in GaInP by destroying the P dimers on the reconstructed surface. Consequently, the understanding of ordering can provide fundamental information about the surface during growth. This paper reports on the use of the surfactant Sb to modulate the order parameter of GaInP to produce disorder-on-order-on-disorder (D/O/D) heterostructures. It was found that heterostructures grown without interruptions have graded interfaces, but heterostructures grown with interruptions have abrupt interfaces. Secondary-ion mass spectroscopy (SIMS) measurements on the heterostructure grown without interruptions indirectly suggests that the Sb surface concentration changed significantly during growth as triethylantimony was added and removed from the system. Consequently, time dependent surface photoabsorption (SPA) measurements were made to determine the change in the P dimer concentration with the addition of triethylantimony. Comparison of the transient time constants with the Langmuir model suggests that relatively high concentrations of Sb accumulate on the surface during growth of the disordered layers. In addition, the results suggest that a critical concentration of Sb on the surface is necessary before the material disorders. Using the surfactant Sb with interruption results in a powerful tool for controlling the surface during growth. This technique was used to produce a GaInP D/O/D heterostructure with a very thin (67 A) ordered layer, sharp interfaces and good photoluminescence. The ability of this tool to produce advanced quantum well devices appears feasible.

Spectroscopic study of surfactant enhanced organometallic vapor phase epitaxy growth of GaInP

Samples of GaxIn1−xP grown by organometallic vapor phase epitaxy on (001) GaAs substrates by addition of TESb demonstrating a lateral superlattice compositional modulation (CM) have been studied by low temperature polarized photoluminescence (PL), power dependent PL, and photoluminescence excitation (PLE) spectroscopy. Strong polarization is observed in the low temperature PL and PLE spectra at Sb concentrations below that where CuPtB ordering is removed and triple period ordering is produced. Low temperature polarized PL is shown to be the most sensitive optical technique for detecting the presence of CM. The radiative recombination mechanism at low temperature is excitonic, originating from the exponential tail of band gap states observed in the PLE spectra. From the measured band gaps, a continuum model of the band structure allows an estimate of an upper limit of the percent modulation present in the samples. Above Sb/III(v)=0.01, compositional modulation is the dominant factor determining the low tem...